Factors Associated With Cardiac Radiation Dose Reduction After Hypofractionated Radiation Therapy for Localized, Left-Sided Breast Cancer in a Large Statewide Quality Consortium

PURPOSE

Limiting cardiac radiation dose is important for minimizing long-term cardiac toxicity in patients with left-sided early-stage breast cancer.

METHODS AND MATERIALS

Prospectively collected dosimetric data were analyzed for patients undergoing moderately hypofractionated radiation therapy to the left breast within the Michigan Radiation Oncology Quality Consortium from 2016 to 2022. The mean heart dose (MHD) goal was progressively tightened from ≤2 Gy in 2016 to MHD ≤ 1.2 Gy in 2018. In 2021, a planning target volume (PTV) coverage goal was added, and the goal MHD was reduced to ≤1 Gy. Multivariate logistic regression models were developed to assess for covariates associated with meeting the MHD goals in 2016 to 2020 and the combined MHD/PTV coverage goal in 2021 to 2022.

RESULTS

In total, 4165 patients were analyzed with a median age of 64 years. Overall average cardiac metric compliance was 91.7%. Utilization of motion management increased from 41.8% in 2016 to 2020 to 46.5% in 2021 to 2022. Similarly, use of prone positioning increased from 12.2% to 22.2% in these periods. On multivariate analysis in the 2016 to 2020 cohort, treatment with motion management (odds ratio [OR], 5.20; 95% CI, 3.59-7.54; P < .0001) or prone positioning (OR, 3.21; 95% CI, 1.85-5.57; P < .0001) was associated with meeting the MHD goal, while receipt of boost (OR, 0.25; 95% CI, 0.17-0.39; P < .0001) and omission of hormone therapy (OR, 0.65; 95% CI, 0.49-0.88; P = .0047) were associated with not meeting the MHD goal. From 2021 to 2022, treatment with motion management (OR, 1.89; 95% CI, 1.12-3.21; P = .018) or prone positioning (OR, 3.71; 95% CI, 1.73-7.95; P = .0008) was associated with meeting the combined MHD/PTV goal, while larger breast volume (≥1440 cc; OR, 0.34; 95% CI, 0.13-0.91; P = .031) was associated with not meeting the combined goal.

CONCLUSIONS

In our statewide consortium, high rates of compliance with aggressive targets for limiting cardiac dose were achievable without sacrificing target coverage.

Partial Breast Irradiation for Patients With Early-Stage Invasive Breast Cancer or Ductal Carcinoma In Situ: An ASTRO Clinical Practice Guideline

PURPOSE

This guideline provides evidence-based recommendations on appropriate indications and techniques for partial breast irradiation (PBI) for patients with early-stage invasive breast cancer and ductal carcinoma in situ.

METHODS

ASTRO convened a task force to address 4 key questions focused on the appropriate indications and techniques for PBI as an alternative to whole breast irradiation (WBI) to result in similar rates of ipsilateral breast recurrence (IBR) and toxicity outcomes. Also addressed were aspects related to the technical delivery of PBI, including dose-fractionation regimens, target volumes, and treatment parameters for different PBI techniques. The guideline is based on a systematic review provided by the Agency for Healthcare Research and Quality. Recommendations were created using a predefined consensus-building methodology and system for grading evidence quality and recommendation strength.

RESULTS

PBI delivered using 3-dimensional conformal radiation therapy, intensity modulated radiation therapy, multicatheter brachytherapy, and single-entry brachytherapy results in similar IBR as WBI with long-term follow-up. Some patient characteristics and tumor features were underrepresented in the randomized controlled trials, making it difficult to fully define IBR risks for patients with these features. Appropriate dose-fractionation regimens, target volume delineation, and treatment planning parameters for delivery of PBI are outlined. Intraoperative radiation therapy alone is associated with a higher IBR rate compared with WBI. A daily or every-other-day external beam PBI regimen is preferred over twice-daily regimens due to late toxicity concerns.

CONCLUSIONS

Based on published data, the ASTRO task force has proposed recommendations to inform best clinical practices on the use of PBI.

Are We Missing Acute Toxicities Associated With Hypofractionated Breast Irradiation? A Report From a Large Multicenter Cohort Study

PURPOSE

The efficacy and long-term safety of hypofractionated whole breast irradiation (HF-WBI) have been established through multiple randomized trials, yet data about acute toxicities remain more limited. Since 2013, our group has prospectively collected acute toxicity data from weekly treatment evaluations and additional assessment after completion. In 2016, we intentionally shifted the posttreatment assessment follow-up visit from 1 month to 2 weeks to evaluate for missed acute toxicity occurring in that immediate posttreatment window. Here, we report whether 2-week follow-up has resulted in increased detection of acute toxicities compared with 4-week follow-up.

METHODS AND MATERIALS

We prospectively compared acute toxicity for patients treated with HF-WBI between January 1, 2013, and August 31, 2015 (4 week follow-up cohort) to patients treated between January 1, 2016, and August 31, 2018 (2 week follow-up cohort). Analyses included a multivariable model that adjusted for other factors known to correlate with toxicity. We prospectively defined acute toxicity as maximum breast pain (moderate or severe rating) and/or occurrence of moist desquamation reported 7 days before the completion of radiation therapy (RT) until 42 days after completion.

RESULTS

A total of 2689 patients who received postlumpectomy radiation and boost were analyzed; 1862 patients in the 2-week follow-up cohort and 827 in the 4-week follow-up cohort. All acute toxicity measures assessed were statistically similar between follow-up cohorts when compared in an unadjusted fashion. Overall acute composite toxicity was 26.4% and 27.7% for patients in the 4-week follow-up and 2-week follow-up cohorts, respectively. Overall acute composite toxicity remained similar between follow-up cohorts in a multivariable, adjusted model and was significantly related to patient's age, body mass index, smoking status, and treatment technique (intensity-modulated RT vs 3-dimensional conformal radiation therapy) but not follow-up cohort.

CONCLUSIONS

An earlier posttreatment follow-up for HF-WBI patients did not reveal a significant increased incidence of acute toxicities at 2 weeks compared with 4 weeks. This study provides physicians and patients with additional data on the safety and tolerability of HF-WBI for early stage breast cancer.

Pectoralis Muscle Dosimetry and Posttreatment Rehabilitation Utilization for Patients With Early-Stage Breast Cancer

PURPOSE

Up to 50% of women treated for localized breast cancer will experience some degree of arm or shoulder morbidity. Although radiation is thought to contribute to this morbidity, the mechanism remains unclear. Prior studies have shown biologic and radiographic changes in the pectoralis muscles after radiation. This study thus aimed to investigate the relationship between radiation to the pectoralis muscles and referrals for rehabilitation services posttreatment for arm and shoulder morbidity.

METHODS AND MATERIALS

A retrospective 1:1 matched case-control study was conducted for patients with breast cancer who were and were not referred for breast or shoulder rehabilitation services between 2014 and 2019 at a single academic institution. Patients were included if they had a lumpectomy and adjuvant radiation. Patients who underwent an axillary lymph node dissection were excluded. Cohorts were matched based on age, axillary surgery, and use of radiation boost. Muscle doses were converted to equivalent dose in 2 Gy fractions assuming an α:β ratio of 2.5 and were compared between the 2 groups.

RESULTS

In our cohort of 50 patients of a median age 60 years (interquartile range, 53-68 years), 36 patients (72%) underwent a sentinel lymph node biopsy in addition to a lumpectomy. Although pectoralis muscle doses were generally higher in those receiving rehabilitation services, this was not statistically significant. Pectoralis major V20-40 Gy reached borderline significance, as did pectoralis major mean dose (17.69 vs 20.89 Gy; P = .06).

CONCLUSIONS

In this limited cohort of patients, we could not definitively conclude a relationship between pectoralis muscle doses and use of rehabilitation services. Given the borderline significant findings, this should be further investigated in a larger cohort.

Cannabis Use Patterns among Patients with Early-Stage Breast Cancer in a Large Multicenter Cohort from a State with Legalized Adult Non-Medical Cannabis

PURPOSE/OBJECTIVE(S)

Cannabis use among patients with cancer is an area of great interest given its widespread acceptance despite the lack of supporting clinical data. The absence of data limits the understanding of potential clinical benefits of cannabis and the ability of providers to deliver evidence-based recommendations for patient care. We explored cannabis use patterns in patients with early-stage breast cancer in a large multicenter cohort in a state with legalized adult non-medical cannabis.

MATERIALS/METHODS

Initial questions about cannabis use history and frequency were introduced in Michigan Radiation Oncology Quality Consortium (MROQC) breast cancer patient surveys on 2/1/2020 for female patients receiving radiation after lumpectomy for non-metastatic breast cancer. Expanded questions were introduced on 6/28/2022 to assess mode of administration, active ingredient, and reason for use. Summary statistics were generated. A multivariable model using logistic regression identified patient characteristics associated with cannabis use.

RESULTS

Among 3948 eligible patients, 2738 (69.35%) completed survey questions, and 2462/2738 (89.9%) completed the initial question on cannabis use. Among those, 364/2462 (14.8%) noted cannabis use in the last 30 days, 588 (23.9%) noted remote use (>30 days ago), 1462 (59.4%) reported never having used cannabis, 44 (1.8%) preferred not to answer cannabis use questions, and 4 (0.4%) did not provide use history. Younger age [age <50 vs 60-70, OR 2.5 (95% CI 1.65, 3.79) p<0.001)], Hispanic ethnicity [OR 2.20 (95% CI 1.06, 4.56) p = 0.03], history of smoking [OR 2.56 (95% CI 1.88, 3.48) p<0.001], current smoking [OR 4.70 (95% CI 3.22, 6.86) p<0.001)], and prior chemotherapy [OR 1.40 (95% CI 1.00, 1.96) p = 0.05] predicted recent cannabis use in a multivariable model. Of the 364 patients endorsing cannabis use in the last 30 days, 89 (24.5%), 72 (19.8%), 29 (8.0%), 66 (18.1%), 30 (8.2%), and 78 (21.4%) reported using cannabis 1-2 days, 3-5 days, 6-9 days, 10-19 days, 20-29 days, and all 30 days, respectively. The most common modes of administration among 76 individuals who responded to the expanded questionnaire to date were oral (39.4%), smoking (30.3%), and topical (10.5%). The products used contained tetrahydrocannabinol (THC; 26.3%), cannabidiol (CBD; 19.7%), balanced levels of THC and CBD (19.7%), or active ingredients that were unknown to the patient (34.2%). Patients frequently endorsed cannabis use for insomnia, anxiety, and pain.

CONCLUSION

Many patients with early-stage breast cancer are using cannabis. Younger age, Hispanic ethnicity, smoking, and chemotherapy history are predictors of cannabis use. Patients are often unaware of the active ingredients in the products that they use, suggesting an important role for patient education and a need to equip providers to advise patients in their care.

Shoulder Muscle Dosimetry and Post-Treatment Rehabilitation Utilization for Early-Stage Breast Cancer Patients

PURPOSE/OBJECTIVE(S)

Rehabilitation services for recovery of impaired physical function following breast cancer treatments are largely underutilized. We previously found that breast cancer survivors treated with radiation who received higher radiation doses to the pectoralis major are more likely to self-report shoulder pain and disability. This study aims to address whether radiation dose delivered to the pectoralis major (Pmaj) and pectoralis minor (Pmin) are correlated with referrals for rehabilitation services post-treatment.

MATERIALS/METHODS

A retrospective 1:1 matched case-control study was conducted for breast cancer patients who were and were not referred for breast or shoulder rehabilitation services between 2014-2019 at a single academic institution. Patients were included if they had a lumpectomy and adjuvant radiation without regional nodal irradiation. Cohorts were matched based on age, axillary surgery (none vs. sentinel lymph node biopsy (SLNB)), and use of radiation boost. We used non-parametric Mann-Whitney U tests to determine whether Pmaj or Pmin doses (mean, V50Gy, V45Gy, V40Gy, V35Gy, V30Gy, V20Gy) were different between the two groups. Muscle doses were converted to EQD2 assuming an α/β ratio of 2.5.

RESULTS

In our study of 30 patients of a median age 57 years (IQR 12.75), 20 (66.67%) patients underwent SLNB in addition to lumpectomy. Median tumor size was 1.1cm (range 0.16 - 7.30cm). Stage was 0 for 11 patients (36.67%), I for 14 patients (46.67%), and II for 5 patients (16.67%). 3D conformal radiation was delivered to the whole breast with a moderately hypofractionated (n = 17) or conventionally fractionated regimen (n = 13). The most common rehabilitation diagnoses were lymphedema (n = 8), scar management (n = 7) and shoulder pain (n = 5). Mean dose to both the Pmaj (20.8Gy vs. 18.6Gy; p = 0.02) and Pmin (30.6Gy vs. 24.6Gy; p = 0.01) were significantly higher in patients who received post-treatment rehabilitation compared to those without. The V40Gy, V35Gy, V30Gy and V20Gy (all p<0.02) for the Pmin and V35Gy, V30Gy and V20Gy for the Pmaj (all p<0.04) were also significantly higher in those who underwent rehabilitation.

CONCLUSION

In this cohort of patients with early-stage breast cancer, increased mean doses to the pectoralis muscles were correlated with increased use of rehabilitation services after radiation. Physicians might consider using these dosimetric data to complement clinical symptoms in the decision-making process for referrals for rehabilitation services. This may help facilitate earlier referral to rehabilitation interventions, which is important since early intervention is correlated with improved shoulder morbidity.

Impact of Breast Volume on Achieving a Conservative Heart and Target Coverage Metric for Patients Receiving Whole Breast Radiotherapy in a Statewide Consortium

PURPOSE/OBJECTIVE(S)

Radiation to large breast volumes (BV) has been associated with increased dose inhomogeneities, breast fibrosis, and induration. Radiation exposure to the heart during breast radiotherapy has been associated with late cardiovascular morbidity and mortality. This study, therefore, investigates the impact of BV on achieving optimal lumpectomy cavity target coverage (V95% [%] >95) while maintaining mean heart dose constraints (MHD, mean [Gy] <1) across a range of BV from patients enrolled in a statewide consortium.

MATERIALS/METHODS

A retrospective analysis was conducted for 2,506 patients receiving left-sided whole breast moderately-hypofractionated (2.5-2.8 Gy/fx) radiotherapy without nodal fields between 2018-2022. The BV was calculated for each patient from contours in the treatment planning system, and the volume distribution partitioned into quartiles. Dosimetric parameters were calculated from dose-volume histograms. The percentage of patients in which the metrics were achieved was calculated for each BV quartile for different treatment positions: all positions, supine, supine with breathing motion management, and prone.

RESULTS

The BV ranges within the quartiles (∼620 patients/quartile) were ≤720.0 cc, 720.1 to ≤1065.0 cc, 1065.1 to ≤1500.0 cc, and >1500.0 cc for quartiles Q1-Q4, respectively. Of the 2,506 patients, 76% were treated supine (of which 41.6% were treated using breathing motion management techniques), 23.5% were treated prone, and 0.5% were treated decubitus. Discrete percentages of patients able to meet the metrics are provided in the table. An increase in BV from Q1 to Q4 correlated with lower percentages of patients meeting the MHD metric, however no correlation was observed between BV and target coverage. Treating supine with breathing motion management resulted in a higher percentage of patients meeting the MHD metric (odds ratio (OR) = 1.96 relative to supine without motion management, p<0.0001), while the prone setup proved to be the superior technique across all quartiles (OR = 3.95 relative to supine, p<0.0001).

CONCLUSION

Increasing BVs resulted in lower percentages of patients receiving MHD≤1 Gy. Thus, cardiac sparing may be more difficult to achieve in patients with larger BV. Utilization of alternate treatment positions, such as supine with breathing motion management and prone, greatly improved the percentage of patients able to meet the MHD metric without sacrificing target coverage in all quartiles. Prone positioning was the technique least susceptible to BV effects in meeting the MHD≤1 Gy goal.

Factors Associated with Cardiac Radiation Dose Reduction Following Hypofractionated Radiation Therapy for Localized, Left-Sided Breast Cancer in a Large Statewide Quality Consortium

PURPOSE/OBJECTIVE(S)

Limiting radiation dose to the heart is important for minimizing the risk of long-term cardiac toxicity in patients with left-sided early-stage breast cancer.

MATERIALS/METHODS

Prospectively collected dosimetric data were analyzed for patients undergoing hypofractionated radiation therapy to the left breast for localized node-negative breast cancer within the Michigan Radiation Oncology Quality Consortium (MROQC) from 2016-2022. Goals for limiting cardiac dose were adjusted over time. From 2016-2020, the cardiac quality metric focused on total mean heart dose (MHD) from the composite whole breast and boost plans, tightening from a goal of MHD ≤2 Gy to MHD ≤1.2 Gy by 2020. In 2021-2022, the cardiac metric transitioned to a combined goal of MHD ≤1.0 Gy from the whole breast plan and ≥95% lumpectomy cavity planning target volume (PTV) receiving 95% of the prescription dose. Separate multivariate logistic regression models were developed to assess for covariates associated with meeting the MHD goal in 2016-2020 and combined MHD/PTV coverage goal in 2021-2022.

RESULTS

In total, 4,165 patients were analyzed with a median age of 64 years. Most patients (86%) had either Tis or T1 disease, and 66% received hormone therapy. Baseline demographic and disease characteristics did not change substantially between treatment periods. Use of breath-hold or motion gating increased from 42% in 2016-2020 to 46% in 2021-2022. Similarly, use of prone positioning increased from 12% to 20%. From 2016-2020, 90.9% of plans achieved the MHD goal, compared to 93.6% of plans achieving the composite MHD/PTV goal from 2021-2022. On multivariate analysis in the 2016-2020 cohort, treatment with motion management (OR 5.20, 95% CI [3.59-7.54], p<0.0001) or prone positioning (OR 3.21, 95% CI [1.85-5.57], p < 0.0001) were associated with meeting the MHD goal, while receipt of boost (OR 0.25, 95% CI [0.17-0.39], p<0.0001) and omission of hormone therapy (OR 0.65, 95% CI [0.49-0.88], p = 0.0047), were associated with not meeting the MHD goal. During the era including composite heart dose and PTV coverage goals (2021-2022), treatment with motion management (OR 1.89, 95% CI [1.12-3.21], p = 0.018) or prone positioning (OR 3.71, 95% CI [1.73-7.95], p = 0.0008) were associated with meeting the combined goal, while larger breast volume (≥1440 cc, OR 0.34, 95% CI [0.13 - 0.91], p = 0.031) and treatment at an academic center (OR 0.36, 95% CI [0.22-0.67], p = 0.0009) were associated with not meeting the combined goal.

CONCLUSION

In our statewide consortium, rates of compliance with aggressive targets for limiting cardiac dose remain high, despite tightening of these goals to include lower mean heart doses and inclusion of a concurrent PTV coverage goal. Treatment using motion management or prone positioning is associated with achieving the cardiac dose goals.

Transcriptomic Analysis to Uncover the Mechanism of Radiosensitization of AR-Positive Triple Negative Breast Cancers with AR Inhibition

PURPOSE/OBJECTIVE(S)

The androgen receptor (AR) has been shown to drive tumor growth in triple negative breast cancers (TNBC), and previous work demonstrated AR inhibition as a strategy for radiosensitization in AR-positive (AR+) TNBC. Despite its role in radioresistance, the mechanistic role of AR in response to radiation therapy (RT) remains unknown, as does the benefit of 2nd generation anti-androgens in this context. We hypothesized that all 2nd generation anti-AR therapy would radiosensitize similarly and that canonical AR transcriptional function was responsible for radioresistance in these models.

MATERIALS/METHODS

Radiosensitization was assessed using 2nd generation AR antagonists (apalutamide, enzalutamide, and darolutamide) using clonogenic survival assays in MDA-MB-453, SUM185, MFM-223, and MDA-MB-231 cells at 2-6Gy. Cellular fractionation experiments were performed and quantitated to determine the location of the AR protein in cells treated with AR agonists +/- RT. RNA Seq was performed and transcriptomic approaches were used (Advaita iPathway analysis) to investigate AR-mediated effects in response to RT.

RESULTS

Inhibition with the 2nd generation anti-androgens enzalutamide and apalutamide is sufficient to radiosensitize AR+ TNBC models (rER: 1.34-1.41); while darolutamide had no effect on radiosensitivity (rER: 0.96-1.11). Additionally, TNBC cells with low AR expression were not radiosensitized by AR inhibition with any drug (rER: 0.96-1.03). While stimulation with the synthetic androgen methyltrienolone R1881 is sufficient to induce nuclear translocation of AR in AR+ TNBC cells, AR inhibition with enzalutamide, apalutamide, or darolutamide blocked AR nuclear translocation under growth conditions with charcoal stripped serum or fetal bovine serum. When cells are treated with R1881+RT, nuclear translocation of AR was induced at similar or greater levels compared to R1881 alone in AR+ TNBC cells. Combination treatment of RT with enzalutamide in the presence of hormones reduced nuclear localization of AR (32-39% reduction) compared to RT alone. RNA-sequencing after RT identified transcriptional changes potentially regulated by AR+RT, including changes in the NHEJ pathway genes. Additionally, pathway analyses in these models demonstrated changes in the MAPK/ERK signaling pathway, among others, that may regulate RT resistance in AR+ TNBC models.

CONCLUSION

Most 2nd generation anti-androgens confer radiosensitization in AR+ TNBC models with cellular localization changes of AR noted after RT. The known structural differences amongst 2nd generation anti-androgens may account for differences in radiosensitization noted. Furthermore, AR-mediated radioresistance may be due, at least in part, to downstream MAPK/ERK signaling. This work builds on the mechanistic understanding of AR-mediated radioresistance in AR+ TNBC and may expose vulnerabilities to overcome resistance to combination treatment with AR inhibition and RT.

NCCN Guidelines® Insights: Breast Cancer, Version 4.2023

The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Breast Cancer address all aspects of management for breast cancer. The treatment landscape of metastatic breast cancer is evolving constantly. The therapeutic strategy takes into consideration tumor biology, biomarkers, and other clinical factors. Due to the growing number of treatment options, if one option fails, there is usually another line of therapy available, providing meaningful improvements in survival. This NCCN Guidelines Insights report focuses on recent updates specific to systemic therapy recommendations for patients with stage IV (M1) disease.

Integrating Tumor-Intrinsic and Immunologic Factors to Identify Immunogenic Breast Cancers from a Low-Risk Cohort: Results from the Randomized SweBCG91RT Trial

PURPOSE

The local immune infiltrate's influence on tumor progression may be closely linked to tumor-intrinsic factors. The study aimed to investigate whether integrating immunologic and tumor-intrinsic factors can identify patients from a low-risk cohort who may be candidates for radiotherapy (RT) de-escalation.

EXPERIMENTAL DESIGN

The SweBCG91RT trial included 1,178 patients with stage I to IIA breast cancer, randomized to breast-conserving surgery with or without adjuvant RT, and followed for a median of 15.2 years. We trained two models designed to capture immunologic activity and immunomodulatory tumor-intrinsic qualities, respectively. We then analyzed if combining these two variables could further stratify tumors, allowing for identifying a subgroup where RT de-escalation is feasible, despite clinical indicators of a high risk of ipsilateral breast tumor recurrence (IBTR).

RESULTS

The prognostic effect of the immunologic model could be predicted by the tumor-intrinsic model (Pinteraction = 0.01). By integrating measurements of the immunologic- and tumor-intrinsic models, patients who benefited from an active immune infiltrate could be identified. These patients benefited from standard RT (HR, 0.28; 95% CI, 0.09-0.85; P = 0.025) and had a 5.4% 10-year incidence of IBTR after irradiation despite high-risk genomic indicators and a low frequency of systemic therapy. In contrast, high-risk tumors without an immune infiltrate had a high 10-year incidence of IBTR despite RT treatment (19.5%; 95% CI, 12.2-30.3).

CONCLUSIONS

Integrating tumor-intrinsic and immunologic factors may identify immunogenic tumors in early-stage breast cancer populations dominated by ER-positive tumors. Patients who benefit from an activated immune infiltrate may be candidates for RT de-escalation.

Abstract 2823: Targeting monopolar spindle kinase I (TTK) as a radiosensitizing strategy in syngeneic murine models of triple negative breast cancer (TNBC) and its implications on the tumor immune microenvironment

Purpose: Triple negative breast cancer (TNBC) is an aggressive breast cancer subset with poor outcomes. Since TNBC is resistant to hormone therapies, there are few effective therapies available for TNBC patients. One potential therapeutic strategy exists in targeting specific molecular components of an individual patient’s cancer. Prior work in our group has nominated monopolar spindle kinase I (TTK) as a gene upregulated in breast cancer patients. Specifically, TTK expression was found to be increased in cancerous breast tissue compared to healthy tissue and correlated with cancer recurrence following radiotherapy. Importantly, the implications of TTK inhibition and radiotherapy on the immune system is not well understood. In this study, we aimed to elucidate the role of combined TTK inhibition and radiotherapy in syngeneic murine mouse models. We hypothesize that TTK inhibition will radiosensitize murine TNBC models to radiotherapy both in vitro and in vivo and modulate the immune tumor microenvironment.

Methods: Cell viability assays were implemented to determine the half-maximal inhibitory concentrations (IC50) of TTK inhibitor. Clonogenic survival assays were used to determine the radiation enhancement ratios (rERs) of TTK inhibition in vitro. Syngeneic murine mouse models were used to assess therapeutic effects of TTK inhibition and RT in vivo. 4T1 TNBC cells were injected bilaterally into the flanks of BALB/c mice and treated with combinations of radiotherapy and TTK inhibition. Tumor growth was monitored and, following the completion of the study, final tumor weights were recorded and tumor tissue was collected to perform immunofluorescent microscopy.

Results: Single-agent TTK inhibition via treatment with the ATP-competitive inhibitor empesertib inhibits the growth of murine TNBC cell lines with IC50 values up to 30nM. Sub-IC50 values of TTK inhibitor induced radiosensitization in the murine TNBC cells 4T1 (rERs ≤ 2.4) and Py8119 (rERs ≤ 1.6). TTK knockdown also resulted in changes in radiosensitization in vitro. Furthermore, we also observed a similar phenotype in vivo. In our 4T1 model system, mice receiving combined treatment had significantly decreased tumor growth compared to mice that receiving single-agent therapies or vehicle control alone. Quantities of monocyte derived suppressor cells and CD8+ T cells were altered with radiotherapy and TTK inhibition.

Conclusion: Our data suggests that TTK inhibition and radiotherapy is synergistic in murine TNBC and alters the tumor immune microenvironment. This combined therapy suggests that changes in the underlying immune mechanisms as a result of the synergistic treatment efficacy are important in TNBC. Future work will examine the underlying mechanisms of TTK inhibition and radiotherapy on systemic and tumoral immune changes.

Citation Format: Kassidy M. Jungles, Zhuwen Wang, Caroline R. Bishop, Kalli R. Jungles, Cydnee Wilson, Meilan Liu, Ashley N. Pearson, Erin A. Holcomb, Ben Chandler, Jadyn James, Amanda Huber, Lori J. Pierce, Corey Speers, James M. Rae, Michael D. Green. Targeting monopolar spindle kinase I (TTK) as a radiosensitizing strategy in syngeneic murine models of triple negative breast cancer (TNBC) and its implications on the tumor immune microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2823.

Increasing Racial and Ethnic Equity, Diversity, and Inclusion in Cancer Treatment Trials: Evaluation of an ASCO-Association of Community Cancer Centers Site Self-Assessment

Clinical trial participants do not reflect the racial and ethnic diversity of people with cancer. ASCO and the Association of Community Cancer Centers collaborated on a quality improvement study to enhance racial and ethnic equity, diversity, and inclusion (EDI) in cancer clinical trials. The groups conducted a pilot study to examine the feasibility, utility, and face validity of a two-part clinical trial site self-assessment to enable diverse types of research sites in the United States to (1) review internal data to assess racial and ethnic disparities in screening and enrollment and (2) review their policies, programs, procedures to identify opportunities and strategies to improve EDI. Overall, 81% of 62 participating sites were satisfied with the assessment; 82% identified opportunities for improvement; and 63% identified specific strategies and 74% thought the assessment had potential to help their site increase EDI. The assessment increased awareness about performance (82%) and helped identify specific strategies (63%) to increase EDI in trials. Although most sites (65%) were able to provide some data on the number of patients that consented, only two sites were able to provide all requested trial screening, offering, and enrollment data by race and ethnicity. Documenting and evaluating such data are critical steps toward improving EDI and are key to identifying and addressing disparities more broadly. ASCO and Association of Community Cancer Centers will partner with sites to better understand their processes and the feasibility of collecting screening, offering, and enrollment data in systematic and automated ways.

Development and Validation of a Genomic Profile for the Omission of Local Adjuvant Radiation in Breast Cancer

PURPOSE

Adjuvant radiotherapy (RT) is used for women with early-stage invasive breast cancer treated with breast-conserving surgery. However, some women with low risk of recurrence may safely be spared RT. This study aimed to identify these women using a molecular-based approach.

METHODS

We analyzed two randomized trials of women with node-negative invasive breast cancer to ± RT following breast-conserving surgery: SweBCG91-RT (stage I-II, no adjuvant systemic therapy) and Princess Margaret (age 50 years or older, T1-T2, adjuvant tamoxifen). Transcriptome-wide profiling was performed (Affymetrix Human Exon 1.0 ST microarray). Patients with estrogen receptor-positive/human epidermal growth factor receptor 2-negative tumors and with gene expression data were included. The SweBCG91-RT cohort was divided into training (N = 243) and validation (N = 354) cohorts. A 16-gene signature named Profile for the Omission of Local Adjuvant Radiation (POLAR) was trained to predict locoregional recurrence (LRR) using elastic net regression. POLAR was then validated in the SweBCG91-RT validation cohort and the Princess Margaret cohort (N = 132).

RESULTS

Patients categorized as POLAR low-risk without RT had a 10-year LRR of 6% (95% CI, 2 to 16) and 7% (0 to 27) in SweBCG91-RT and Princess Margaret cohorts, respectively. There was no significant benefit from RT in POLAR low-risk patients (hazard ratio [HR], 1.1 [0.39 to 3.4], P = .81, and HR, 1.5 [0.14 to 16], P = .74, respectively). Patients categorized as POLAR high-risk had a significant decreased risk of LRR with RT (HR, 0.43 [0.24 to 0.78], P = .0055, and HR, 0.25 [0.07 to 0.92], P = .038, respectively). An exploratory analysis testing for interaction between RT and POLAR in the combined validation cohort was performed (P = .066).

CONCLUSION

The novel POLAR genomic signature on the basis of LRR biology may identify patients with a low risk of LRR despite not receiving RT, and thus may be candidates for RT omission.

Updates in combined approaches of radiotherapy and immune checkpoint inhibitors for the treatment of breast cancer

Breast cancer is the most prevalent non-skin cancer diagnosed in females and developing novel therapeutic strategies to improve patient outcomes is crucial. The immune system plays an integral role in the body’s response to breast cancer and modulating this immune response through immunotherapy is a promising therapeutic option. Although immune checkpoint inhibitors were recently approved for the treatment of breast cancer patients, not all patients respond to immune checkpoint inhibitors as a monotherapy, highlighting the need to better understand the biology underlying patient response. Additionally, as radiotherapy is a critical component of breast cancer treatment, understanding the interplay of radiation and immune checkpoint inhibitors will be vital as recent studies suggest that combined therapies may induce synergistic effects in preclinical models of breast cancer. This review will discuss the mechanisms supporting combined approaches with radiotherapy and immune checkpoint inhibitors for the treatment of breast cancer. Moreover, this review will analyze the current clinical trials examining combined approaches of radiotherapy, immunotherapy, chemotherapy, and targeted therapy. Finally, this review will evaluate data regarding treatment tolerance and potential biomarkers for these emerging therapies aimed at improving breast cancer outcomes.

The HAPPE plus Event-Related (HAPPE+ER) software: A standardized preprocessing pipeline for event-related potential analyses

Event-Related Potential (ERP) designs are a common method for interrogating neurocognitive function with electroencephalography (EEG). However, the traditional method of preprocessing ERP data is manual-editing - a subjective, time-consuming processes. A number of automated pipelines have recently been created to address the need for standardization, automation, and quantification of EEG data pre-processing; however, few are optimized for ERP analyses (especially in developmental or clinical populations). We propose and validate the HAPPE plus Event-Related (HAPPE+ER) software, a standardized and automated pre-processing pipeline optimized for ERP analyses across the lifespan. HAPPE+ER processes event-related potential data from raw files through preprocessing and generation of event-related potentials for statistical analyses. HAPPE+ER also includes post-processing reports of both data quality and pipeline quality metrics to facilitate the evaluation and reporting of data processing in a standardized manner. Finally, HAPPE+ER includes post-processing scripts to facilitate validating HAPPE+ER performance and/or comparing to performance of other preprocessing pipelines in users' own data via simulated ERPs. We describe multiple approaches with simulated and real ERP data to optimize pipeline performance and compare to other methods and pipelines. HAPPE+ER software is freely available under the terms of GNU General Public License at https://www.gnu.org/licenses/#GPL.

Androgen and oestrogen receptor co-expression determines the efficacy of hormone receptor-mediated radiosensitisation in breast cancer

PURPOSE

Radiation therapy (RT) and hormone receptor (HR) inhibition are used for the treatment of HR-positive breast cancers; however, little is known about the interaction of the androgen receptor (AR) and estrogen receptor (ER) in response to RT in AR-positive, ER-positive (AR+/ER+) breast cancers. Here we assessed radiosensitisation of AR+/ER+ cell lines using pharmacologic or genetic inhibition/degradation of AR and/or ER.

METHODS

Radiosensitisation was assessed with AR antagonists (enzalutamide, apalutamide, darolutamide, seviteronel, ARD-61), ER antagonists (tamoxifen, fulvestrant) or using knockout of AR.

RESULTS

Treatment with AR antagonists or ER antagonists in combination with RT did not result in radiosensitisation changes (radiation enhancement ratios [rER]: 0.76-1.21). Fulvestrant treatment provided significant radiosensitisation of CAMA-1 and BT-474 cells (rER: 1.06-2.0) but not ZR-75-1 cells (rER: 0.9-1.11). Combining tamoxifen with enzalutamide did not alter radiosensitivity using a 1 h or 1-week pretreatment (rER: 0.95-1.14). Radiosensitivity was unchanged in AR knockout compared to Cas9 cells (rER: 1.07 ± 0.11), and no additional radiosensitisation was achieved with tamoxifen or fulvestrant compared to Cas9 cells (rER: 0.84-1.19).

CONCLUSION

While radiosensitising in AR + TNBC, AR inhibition does not modulate radiation sensitivity in AR+/ER+ breast cancer. The efficacy of ER antagonists in combination with RT may also be dependent on AR expression.

In pursuit of equity in cancer care: moving beyond the Affordable Care Act

Although Medicaid Expansion under the Patient Protection and Affordable Care Act (ACA) has been associated with many improvements for patients with cancer, Snyder et al. provide evidence demonstrating the persistence of racial disparities in cancer. This Editorial describes why insurance coverage alone does not ensure access to health care, highlights various manifestations of structural racism that constitute barriers to access beyond the direct costs of care, and calls for not just equality, but equity, in cancer care.

Bcl-xL inhibition radiosensitizes PIK3CA/PTEN wild-type triple negative breast cancers with low Mcl-1 expression

Patients with radioresistant breast cancers, including a large percentage of women with triple negative breast cancer (TNBC), demonstrate limited response to radiation (RT) and increased locoregional recurrence; thus, strategies to increase the efficacy of RT in TNBC are critically needed. We demonstrate that pan Bcl-2 family inhibition (ABT-263, rER: 1.52-1.56) or Bcl-xL specific inhibition (WEHI-539, A-1331852; rER: 1.31-2.00) radiosensitized wild-type PIK3CA/PTEN TNBC (MDA-MB-231, CAL-120) but failed to radiosensitize mutant PIK3CA/PTEN TNBC (rER: 0.90 - 1.07; MDA-MB-468, CAL-51, SUM-159). Specific inhibition of Bcl-2 or Mcl-1 did not induce radiosensitization, regardless of PIK3CA/PTEN status (rER: 0.95 - 1.07). In wild-type PIK3CA/PTEN TNBC, pan Bcl-2 family inhibition or Bcl-xL specific inhibition with RT led to increased levels of apoptosis (p < 0.001) and an increase in cleaved PARP and cleaved caspase 3. CRISPR-mediated PTEN knockout in wild-type PIK3CA/PTEN MDA-MB-231 and CAL-120 cells induced expression of pAKT/Akt and Mcl-1 and abolished Bcl-xL inhibitor-mediated radiosensitization (rER: 0.94 - 1.07). Similarly, Mcl-1 overexpression abolished radiosensitization in MDA-MB-231 and CAL-120 cells (rER: 1.02 - 1.04) but transient MCL1 knockdown in CAL-51 cells promoted Bcl-xL-inhibitor mediated radiosensitization (rER 2.35 ± 0.05). In vivo, ABT-263 or A-1331852 in combination with RT decreased tumor growth and increased tumor tripling time (p < 0.0001) in PIK3CA/PTEN wild-type TNBC cell line and patient-derived xenografts. Collectively, this study provides the preclinical rationale for early phase clinical trials testing the safety, tolerability, and efficacy of Bcl-xL inhibition and RT in women with wild-type PIK3CA/PTEN wild-type TNBC at high risk for recurrence.

Abstract 2697: Inhibition of estrogen receptor signaling as a strategy for radiosensitization of ER+ breast cancers

Purpose: The estrogen receptor (ER) is expressed in over 80% of breast tumors and has been shown to be a significant driver of breast cancer (BC) pathogenesis and therefore a target of effective first-line therapies. While both ionizing radiation (RT) and endocrine therapies (ET) are used for the treatment of ER+ BC, the effect of ET on tumor radiosensitization remains unclear, with concerns it may be radioprotective based on G1 cell arrest with ET treatment. Here we assessed the efficacy and mechanism of ER-mediated radiosensitization using various pharmacologic approaches in ER+ BC.

Methods: Radiosensitization with ER inhibitors (tamoxifen [TAM], fulvestrant [FULV], AZD9496) was assessed using clonogenic survival assays. DNA damage was assessed by the neutral comet assay. Efficiency of homologous recombination (HR) or non-homologous end joining (NHEJ) as well as changes in cell cycle, apoptosis, and senescence were assessed. The efficacy of TAM with RT in vivo was assessed with an MCF-7 xenograft model.

Results: The selective estrogen receptor modulator TAM radiosensitized ER+ MCF-7 (enhancement ratio [enhR]: 1.14-1.50) and T47D (enhR: 1.33-1.60) cells but not ER-negative SUM-159 cells (enhR: 0.99-1.02). The selective estrogen receptor degrader (SERD) FULV had similar radiosensitization effects in MCF-7 (enhR: 1.33-1.76) and T47D cells (enhR: 0.97-2.81) with no radiosensitization observed in SUM-159 cells (enhR: 1.01-1.03). The novel oral SERD AZD9496 radiosensitized MCF-7 cells (enhR: 1.36-1.56). MCF-7 cells treated with TAM and RT had an increase in dsDNA breaks compared to RT alone as measured by the comet assay (p&lt;0.05) and a decrease in NHEJ-mediated repair with TAM (p&lt;0.05). No changes were observed in HR-mediated repair by Rad51 foci or a reporter (p=NS). RT alone and in combination with TAM or FULV induced similar levels of cell cycle arrest, suggesting that radiosensitization with the combination therapy is cell-cycle independent. There were no significant changes in apoptosis with TAM, FULV, RT, or the combination (p=NS). Although TAM or FULV did induce senescence, ET with RT increased senescence induction (p&lt;0.05). In vivo, combination RT and TAM led to a significant delay in days to tumor doubling (control: 17, TAM: 40, RT: 32, TAM+RT: undefined; p&lt;0.0001), and a significant difference in tumor growth between mice treated with TAM or RT alone compared combination treatment, with no increased toxicities or skin lesions from the combination treatment. Conclusion: Our data suggest that TAM, FULV, or AZD9496 can radiosensitize ER+ breast tumors, and these agents with RT may be more effective for radiosensitization. This work also supports further clinical investigation of the timing of RT for patients receiving ET, including using ET during RT, especially as initiating ET prior to RT has been increasingly utilized as a bridging therapy followed by concurrent ET+RT during the COVID-19 pandemic.

Citation Format: Anna R. Michmerhuizen, Lynn M. Lerner, Andrea M. Pesch, Connor Ward, Rachel Schwartz, Kari Wilder-Romans, Meilan Liu, Charles Nino, Kassidy Jungles, Ruth Azaria, Alexa Jelley, Nicole Zambrana Garcia, Alexis Harold, Amanda Zhang, Bryan Wharram, Daniel F. Hayes, James M. Rae, Lori J. Pierce, Corey W. Speers. Inhibition of estrogen receptor signaling as a strategy for radiosensitization of ER+ breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2697.

Abstract 3307: Multiomics analysis to uncover the mechanism of radiosensitization of AR-positive triple negative breast cancers with AR inhibition

Purpose: Expression of the androgen receptor (AR) has been identified as a driver of tumor growth in triple negative breast cancers (TNBC), and previous work has nominated AR inhibition as a strategy for radiosensitization in AR+ TNBC. Despite its role in radioresistance in AR+ TNBC, the mechanistic role of AR and specifically its role in mediating DNA damage repair in response to radiation therapy (RT) remains unknown.

Methods: Nuclear fractionation experiments were performed to assess cellular localization of AR protein in AR+ TNBC cell lines (ACC-422, MDA-MB-453). Cells were cultured in media containing hormones (FBS) with treatment of enzalutamide (ENZA), apalutamide (APA), or darolutamide (DARO). Cells were alternatively cultured in media containing charcoal stripped serum (CSS) without hormones with R1881 stimulation. RNA-sequencing was performed to compare AR+ TNBC cells treated with CSS or R1881 stimulation alone or in combination with ionizing radiation. Reverse phase protein arrays were performed in cells treated with ENZA, RT, or combination treatment.

Results: While stimulation with R1881 was sufficient to induce nuclear translocation of AR in MDA-MB-453 cells, AR inhibition with ENZA, APA, or DARO blocked AR nuclear translocation under CSS or FBS growth conditions. When cells were treated with R1881+RT, AR nuclear translocation was induced at similar or greater levels compared to R1881 alone in MDA-MB-453 and ACC-422 cells. Combination treatment of RT with ENZA in the presence of hormones reduced AR nuclear localization (39% reduction in MDA-MB-453 cells and 32% reduction in ACC-422 cells) compared to RT alone. These results suggest that decreased promoter region binding, and gene expression upregulation may be a mechanism of radiosensitization with AR inhibition. In addition, transcriptomic analyses demonstrated at least 979 genes differentially expressed in multiple models. Pathway analyses in these models showed common affected pathways included ECM-receptor interaction, PPAR-gamma activation, PI3K-Akt signaling pathway, and the MAPK/ERK signaling pathway. Proteomic analysis in the same cell lines identified apoptosis, DNA damage, and cell cycle pathway changes after RT when AR-signaling was blocked. Common affected pathways in combined analyses identified PI3K-Akt and MAPK/ERK signaling pathway changes that may be responsible for this radiosensitizing phenotype.

Conclusions: Our data suggest that AR inhibition in AR+ TNBC is sufficient to inhibit AR nuclear translocation suggesting that AR may play a nuclear role in response to RT to promote DNA repair and radioresistance. We identify potential pathways, including ECM-receptor interaction, PI3K-Akt signaling pathway, and the MAPK/ERK signaling pathway that may be regulated by AR in response to RT and therefore may be responsible for radioresistance.

Citation Format: Anna R. Michmerhuizen, Andrea M. Pesch, Benjamin C. Chandler, Lynn M. Lerner, Connor Ward, Leah Moubadder, Stephanie The, Breanna McBean, Caleb Cheng, Lori J. Pierce, Corey W. Speers. Multiomics analysis to uncover the mechanism of radiosensitization of AR-positive triple negative breast cancers with AR inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3307.

Abstract 216: Expression of DNA damage response proteins modifies the efficacy of CDK4/6 inhibitor-mediated radiosensitization in breast cancer models

Purpose: CDK4/6 inhibitors (CDK4/6i) are standard of care for the treatment of locally advanced and metastatic estrogen receptor-positive (ER+), HER2-negative metastatic breast cancer (BC). CDK4/6 inhibition + radiation therapy (RT) is synergistic in both ER+ and triple negative breast cancers (TNBC), but the underlying mechanism is not entirely understood. In this study, we evaluated how pre-existing or genetically engineered deficits in DNA damage response genes (BRCA1/2, RAD51, RB1, XRCC6, TP53) influence radiosensitization. We hypothesized that inhibition of homologous recombination (HR) would prevent CDK4/6i-mediated radiosensitization and blocking non-homologous end joining (NHEJ) would be synergistic.

Methods: Cellular proliferation assays determined the half-maximal inhibitory concentrations (IC50) of the 3 approved CDK4/6i palbociclib, ribociclib, and abemaciclib. Clonogenic survival assays determined the radiation enhancement ratios (rERs) and evaluated the efficacy of CDK4/6i + RT. Immunofluorescence assays measured RAD51 foci formation and quantified micronuclei formation following RT and/or CDK4/6 inhibition. Immunoprecipitation with myc-RAD51 and GFP-RB assessed potential protein-protein interactions.

Results: While ER+ and TNBC cell lines with wild type BRCA1 expression are radiosensitized by CDK4/6i, BRCA1-deficient SUM-149 cells are not radiosensitized by CDK4/6i at concentrations up to 1µM (rER: 0.92-1.01). In an MCF-7 isogenic model of BRCA2 knockout, CDK4/6i-mediated radiosensitization was abolished compared to Cas9 control or parental cell lines. In ER+ BC cell lines (MCF-7-p53 wt, T47D-p53 mutant), transient or genetic knockdown of RAD51 prevented CDK4/6i-induced radiosensitization. The total quantity of RT-induced RAD51 foci increased in vitro following overexpression of RB-a tumor suppressor and downstream target of CDK4/6. RB overexpression also rescued CDK4/6i-mediated radiosensitization in RB-deficient cell lines through changes in HR efficiency but not via NHEJ or altered micronuclei formation. Moreover, immunoprecipitation of RAD51 in ER+ (MCF-7) and TNBC (MDA-MB-231) cells exhibited an interaction with RB. Conversely, loss of the NHEJ-associated protein Ku70 (XRCC6) was synergistic with palbociclib + RT in MCF7 (rER: 1.76-2.44) and T47D (rER: 1.61-3.88) cells. Finally, CRISPR Cas9-mediated loss of the tumor suppressor p53 (TP53) did not affect radiosensitization induced by CDK4/6i in isogenic p53 wt ER+ (MCF-7, rER: 1.19-1.33) and p53 wt TNBC (CAL-51, rER: 1.23-1.52) cell lines with TP53 loss.

Conclusions: Taken together, our results in multiple non-overlapping isogenic models of ER+ and TNBC suggest that CDK4/6i-mediated radiosensitization of BC cell lines occurs through impaired HR activity and RB signaling, and not through the actions of p53 or NHEJ-mediated DNA repair.

Citation Format: Kassidy M. Jungles, Andrea M. Pesch, Nicole Hirsh, Anna R. Michmerhuizen, Kari Wilder-Romans, Benjamin C. Chandler, Meilan Liu, Lynn Lerner, Lori J. Pierce, James M. Rae, Corey W. Speers. Expression of DNA damage response proteins modifies the efficacy of CDK4/6 inhibitor-mediated radiosensitization in breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 216.

Breast Cancer, Version 3.2022, NCCN Clinical Practice Guidelines in Oncology

The therapeutic options for patients with noninvasive or invasive breast cancer are complex and varied. These NCCN Clinical Practice Guidelines for Breast Cancer include recommendations for clinical management of patients with carcinoma in situ, invasive breast cancer, Paget disease, phyllodes tumor, inflammatory breast cancer, and management of breast cancer during pregnancy. The content featured in this issue focuses on the recommendations for overall management of ductal carcinoma in situ and the workup and locoregional management of early stage invasive breast cancer. For the full version of the NCCN Guidelines for Breast Cancer, visit NCCN.org.

Assessing feasibility and utility of an implicit bias training program for addressing disparities in cancer clinical trial participation

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Background: Low participation of Black, Hispanic, Latinx and other underrepresented racial/ethnic groups in clinical research remains a problem across the U.S. Recent studies have highlighted that stereotypes, assumptions, and bias play a role in lack of diversity in cancer trial participation. To help address this, the Association of Community Cancer Centers (ACCC) and American Society of Clinical Oncology (ASCO) piloted an implicit bias training program for clinical research teams. Methods: Adapted from the Duke University Just Ask™ program, the pilot program is comprised of eLearning modules which can be completed in about 60 minutes. Features include education on diversity, equity, and bias in clinical trial participation, case vignettes, and strategies to mitigate disparities. A call was issued to members of both organizations. After completing the training, all individual participants were asked to complete a retrospective pre/post survey to assess change in knowledge and attitude. Focus groups explored participants’ experience with the training. Another survey was administered 6 weeks later to assess sustainability of changes. Results: Research teams from 50 programs were selected for the pilot. 129 individuals consented, and 126 completed the training and evaluations (98% response rate). 48% of participants reported that they had completed training on implicit bias and/or related topics prior to the pilot. Increased levels of knowledge were reported across all key training concepts, with an average % increase from 19% to 45%. Similar increases were observed for strategies for addressing implicit bias, with an average % increase from 10% to 31%. At 6 weeks post-training, there was a slight decrease in knowledge across most items, from -1% to -8%. Most (92%) participants reported satisfaction with the course, and most (92%) indicated they would recommend it to a colleague and would recommend implementing it at their program. Suggestions to improve the course included streamlining content and providing additional tools and resources. Conclusions: Pilot findings support the feasibility and utility of the training, which can help cancer programs to address disparities in clinical research. Next steps include modifying the course based on participant feedback, disseminating the training and supplementary resources, and exploring options for assessing the impact on upstream outcomes such as diversity in trial participation.[Table: see text]

Availability of data for screening, offering, and consenting patients to cancer clinical trials: Report from an ASCO-ACCC collaboration

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Background: Only a small fraction of patients with cancer participate in treatment trials. Patients identifying as members of racial and ethnic minority groups are consistently underrepresented in these trials. A recent systematic review reported that patients, regardless of race and ethnicity, are willing to enroll in trials if asked to participate by their treating clinician. Prospective and longitudinal data and metrics at the site- and clinician-level are necessary to understand whether patients are equitably considered for clinical trials. Methods: ASCO and Association of Community Cancer Centers (ACCC) developed a self-assessment for trial sites to record and gauge the number of patients across races and ethnicities screened, offered, and enrolled into clinical trials. Research sites, from across the US, were recruited through an open call to apply to participate in the ASCO-ACCC Pilot Project. There were 65 sites assigned to this pilot study, which tested the feasibility and utility of the site assessment. Sites were asked to enter 2019 and 2020 aggregate data for each step along the clinical trial enrollment continuum by select races and ethnicities (Black, Hispanic/Latinx, White) and overall. Results: 62 of 65 sites completed the study and represented a range of settings and practice types (61% academic, 26% hospital/health system, 13% independent). Only 2 sites (3%) were able to provide the data requested at each enrollment step in the assessment (table). Sites that collected the data did not do so routinely (table) and most had to compile data through multiple sources and/or manual extraction (40-100% across enrollment steps). Sites with missing data reported they did not collect data at all (36-64% across enrollment steps), did not collect data in a systematic way (0-29% across enrollment steps), or stated it would be too burdensome to manually review charts to extract data (12-29% across enrollment steps). Conclusions: Data collection and routine evaluation of participation metrics, by race and ethnicity, are necessary to assess and monitor equity and diversity in clinical trials. Most sites in this study did not collect, or routinely collect, data for screening, offering, and consenting patients to clinical trials. Without these data, sites are unable to evaluate and monitor whether their patients have equitable access to clinical trials or establish strategies to address any inequities. ASCO and ACCC will continue to partner with sites to better understand their processes and the feasibility of collecting such data in a systematic and automated way, such as through electronic health record systems. [Table: see text]

Increasing Racial and Ethnic Diversity in Cancer Clinical Trials: An American Society of Clinical Oncology and Association of Community Cancer Centers Joint Research Statement

A concerted commitment across research stakeholders is necessary to increase equity, diversity, and inclusion (EDI) and address barriers to cancer clinical trial recruitment and participation. Racial and ethnic diversity among trial participants is key to understanding intrinsic and extrinsic factors that may affect patient response to cancer treatments. This ASCO and Association of Community Cancer Centers (ACCC) Research Statement presents specific recommendations and strategies for the research community to improve EDI in cancer clinical trials. There are six overarching recommendations: (1) clinical trials are an integral component of high-quality cancer care, and every person with cancer should have the opportunity to participate; (2) trial sponsors and investigators should design and implement trials with a focus on reducing barriers and enhancing EDI, and work with sites to conduct trials in ways that increase participation of under-represented populations; (3) trial sponsors, researchers, and sites should form long-standing partnerships with patients, patient advocacy groups, and community leaders and groups; (4) anyone designing or conducting trials should complete recurring education, training, and evaluation to demonstrate and maintain cross-cultural competencies, mitigation of bias, effective communication, and a commitment to achieving EDI; (5) research stakeholders should invest in programs and policies that increase EDI in trials and in the research workforce; and (6) research stakeholders should collect and publish aggregate data on racial and ethnic diversity of trial participants when reporting results of trials, programs, and interventions to increase EDI. The recommendations are intended to serve as a guide for the research community to improve participation rates among people from racial and ethnic minority populations historically under-represented in cancer clinical trials. ASCO and ACCC will work at all levels to advance the recommendations in this publication.

Attention to diet, exercise, and weight in oncology care: Results of an American Society of Clinical Oncology national patient survey

BACKGROUND

The American Society of Clinical Oncology (ASCO) surveyed cancer patients to assess practice patterns related to weight, diet, and exercise as a part of cancer care.

METHODS

An online survey was distributed between March and June 2020 through ASCO channels and patient advocacy organizations. Direct email communication was sent to more than 25,000 contacts, and information about the survey was posted on Cancer.Net. Eligibility criteria included being aged at least 18 years, living in the United States, and having been diagnosed with cancer. Logistic regression was used to determine factors associated with recommendation and referral patterns.

RESULTS

In total, 2419 individuals responded to the survey. Most respondents were female (60.1%), 61.1% had an early-stage malignancy, and 48.4% were currently receiving treatment. Breast cancer was the most common cancer (35.7%). The majority of respondents consumed ≤2 servings of fruits and vegetables/d (50.5%) and exercised ≤2 times/wk (50.1%). Exercise was addressed at most or some oncology visits in 56.8% of respondents, diet in 50.1%, and weight in 28.0%. Respondents whose oncology provider provided diet and/or exercise recommendations were more likely to report changes in these behaviors vs. those whose oncology provider did not (exercise: 79.6% vs 69.0%, P < .001; diet 81.1% vs 71.3%, P < .001; weight 81.0% vs 73.3%, P = .003).

CONCLUSIONS

In a national survey of oncology patients, slightly more than one-half reported attention to diet and exercise during oncology visits. Provider recommendations for diet, exercise, and weight were associated with positive changes in these behaviors, reinforcing the importance of attention to these topics as a part of oncology care.

Uptake of Adjuvant Durvalumab After Definitive Concurrent Chemoradiotherapy for Stage III Nonsmall-cell Lung Cancer

OBJECTIVES

The addition of adjuvant durvalumab improves overall survival in locally advanced nonsmall-cell lung cancer (NSCLC) patients treated with definitive chemoradiation, but the real-world uptake of adjuvant durvalumab is unknown.

MATERIALS AND METHODS

We identified patients with stage III NSCLC treated with definitive concurrent chemoradiation from January 2018 to October 2020 from a statewide radiation oncology quality consortium, representing a mix of community (n=22 centers) and academic (n=5) across the state of Michigan. Use of adjuvant durvalumab was ascertained at the time of routine 3-month or 6-month follow-up after completion of chemoradiation.

RESULTS

Of 421 patients with stage III NSCLC who completed chemoradiation, 322 (76.5%) initiated adjuvant durvalumab. The percentage of patients initiating adjuvant durvalumab increased over time from 66% early in the study period to 92% at the end of the study period. There was substantial heterogeneity by treatment center, ranging from 53% to 90%. In multivariable logistic regression, independent predictors of durvalumab initiation included more recent month (odds ratio [OR]: 1.05 per month, 95% confidence interval [CI]: 1.02-1.08, P=0.003), lower Eastern Cooperative Oncology Group score (OR: 4.02 for ECOG 0 vs. 2+, 95% CI: 1.67-9.64, P=0.002), and a trend toward significance for female sex (OR: 1.66, 95% CI: 0.98-2.82, P=0.06).

CONCLUSION

Adjuvant durvalumab for stage III NSCLC treated with definitive chemoradiation was rapidly and successfully incorporated into clinical care across a range of community and academic settings in the state of Michigan, with over 90% of potentially eligible patients starting durvalumab in more recent months.

Comparative Effectiveness Analysis of 3D-Conformal Radiation Therapy Versus Intensity Modulated Radiation Therapy (IMRT) in a Prospective Multicenter Cohort of Patients With Breast Cancer

PURPOSE

Simple intensity modulation of radiation therapy reduces acute toxicity compared with 2-dimensional techniques in adjuvant breast cancer treatment, but it remains unknown whether more complex or inverse-planned intensity modulated radiation therapy (IMRT) offers an advantage over forward-planned, 3-dimensional conformal radiation therapy (3DCRT).

METHODS AND MATERIALS

Using prospective data regarding patients receiving adjuvant whole breast radiation therapy without nodal irradiation at 23 institutions from 2011 to 2018, we compared the incidence of acute toxicity (moderate-severe pain or moist desquamation) in patients receiving 3DCRT versus IMRT (either inverse planned or, if forward-planned, using ≥5 segments per gantry angle). We evaluated associations between technique and toxicity using multivariable models with inverse-probability-of-treatment weighting, adjusting for treatment facility as a random effect.

RESULTS

Of 1185 patients treated with 3DCRT and conventional fractionation, 650 (54.9%) experienced acute toxicity; of 774 treated with highly segmented forward-planned IMRT, 458 (59.2%) did; and of 580 treated with inverse-planned IMRT, 245 (42.2%) did. Of 1296 patients treated with hypofractionation and 3DCRT, 432 (33.3%) experienced acute toxicity; of 709 treated with highly segmented forward-planned IMRT, 227 (32.0%) did; and of 623 treated with inverse-planned IMRT, 164 (26.3%) did. On multivariable analysis with inverse-probability-of-treatment weighting, the odds ratio for acute toxicity after inverse-planned IMRT versus 3DCRT was 0.64 (95% confidence interval, 0.45-0.91) with conventional fractionation and 0.41 (95% confidence interval, 0.26-0.65) with hypofractionation.

CONCLUSIONS

This large, prospective, multicenter comparative effectiveness study found a significant benefit from inverse-planned IMRT compared with 3DCRT in reducing acute toxicity of breast radiation therapy. Future research should identify the dosimetric differences that mediate this association and evaluate cost-effectiveness.

Racial Differences in Treatments and Toxicity in Patients With Non-Small-Cell Lung Cancer Treated With Thoracic Radiation Therapy

PURPOSE

Historical racial disparities in lung cancer surgery rates resulted in lower survival in Black patients. Our objective was to examine racial differences in thoracic radiation treatments and toxicities in patients with non-small-cell lung cancer.

METHODS AND MATERIALS

A large institutional review board-approved statewide patient-level database of patients with stage II-III non-small-cell lung cancer who received definitive thoracic radiation from March 2012 to November 2019 was analyzed to assess associations between race and other variables. Race (White or Black) was defined by patient self-report. Provider-reported toxicity was defined by Common Terminology Criteria for Adverse Events version 4.0. Patient-reported toxicity was determined by the Functional Assessment of Cancer Therapy-Lung quality-of-life instrument. Univariable and multivariable regression models were fitted to assess relationships between race and variables of interest. Spearman rank-correlation coefficients were calculated between provider-reported toxicity and similar patient-reported outcomes.

RESULTS

One thousand four hundred forty-one patients from 24 institutions with mean age 68 years (range, 38-94 years) were evaluated. Race was not significantly associated with radiation or chemotherapy approach. There was significantly increased patient-reported general pain in Black patients at the preradiation and end-of-radiation time points. Black patients were significantly less likely to have provider-reported grade 2+ pneumonitis (odds ratio 0.36, P = .03), even after controlling for known patient and treatment factors. Correlation coefficients between provider- and patient-reported toxicities were generally similar across race groups except for a stronger correlation between patient- and provider-reported esophagitis in White patients.

CONCLUSION

In this large multi-institutional study, we found no evidence of racial differences in radiation treatment or chemotherapy approaches. We did, however, unexpectedly find that Black race was associated with lower odds of provider-reported grade 2+ radiation pneumonitis. The stronger correlation between patient- and provider-reported esophagitis and swallowing symptoms for White patients also suggests possible under-recognition of symptoms in Black patients. Further research is needed to study the implications for Black patients.

Abstract P4-02-04: Endocrine therapy treatment radiosensitizes estrogen receptor-positive breast cancers

Purpose: Estrogen receptor (ER) expression is present in over 80% of breast tumors and has been shown to be a significant driver of breast cancer (BC) pathogenesis and therefore a target of first-line therapies for ER-positive (ER+) BC patients. While both ionizing radiation (RT) and endocrine therapies (ET) are used for the treatment of ER+ BC, the sequencing of therapy and the effect of ET on tumor radiosensitization remain unclear. Recently, this question has become much more clinically relevant when many physicians started offering ET as a bridging strategy to surgery and RT during the COVID-19 pandemic. Here we assessed the efficacy and mechanism of ER inhibition in ER+ BC in combination with RT in preclinical models. Methods: Clonogenic survival assays were used to assess radiosensitization. Inhibition of ER signaling was accomplished by treating ER+ MCF-7 and T47D cells with the selective ER modulator (SERM), tamoxifen, or the selective ER degrader (SERD), fulvestrant. The ER-negative SUM-159 cells were used as a negative control. DNA damage was assessed by the neutral comet assay. Efficiency of homologous recombination (HR) was measured by Rad51 foci or a GFP reporter system. Non-homologous end joining (NHEJ) efficiency was assessed with a pEYFP reporter. Cell cycle effects were measured using flow cytometry with propidium iodide (PI) staining. Apoptosis was assessed by annexin V/PI via flow cytometry. Senescence was measured using β-galactosidase staining. Western blotting was used to quantify expression of proteins and phospho-proteins involved in cell cycle and apoptosis. An MCF-7 xenograft model was used to assess the efficacy of tamoxifen with RT in vivo. Synergy was determined using the fractional tumor volume (FTV) method. Results: ER inhibition with tamoxifen radiosensitized ER+ MCF-7 (10-250 nM, enhR: 1.14-1.50) and T47D (500 nM-2.0 µM, enhR: 1.33-1.60) cells but not ER-negative SUM-159 cells (500 nM-2.0 µM, enhR: 0.99-1.02). ER degradation with fulvestrant had similar radiosensitization effects in MCF-7 (1-25 nM, enhR: 1.33-1.76) and T47D cells (0.5-5 nM, enhR: 0.97-2.81) with no radiosensitization observed in SUM-159 cells (1-25 nM, enhR: 1.01-1.03). MCF-7 cells treated with 500 nM tamoxifen and 4 Gy RT had an increase in dsDNA breaks compared to RT alone as measured by the comet assay (p&lt;0.05), and there was a decrease in NHEJ-mediated repair with tamoxifen treatment (p&lt;0.05). No changes were observed in HR-mediated repair by Rad51 foci or an HR reporter (p=NS). RT alone and in combination with tamoxifen and fulvestrant induced similar levels of cell cycle arrest, suggesting that radiosensitization with the combination therapy is a cell-cycle independent effect. In addition, there were no significant changes in apoptosis in MCF-7 or T47D cells with endocrine therapy, RT, or the combination (p=NS). Although treatment with ET did induce senescence in ER+ MCF-7 and T47D cells, the combination treatment of ET with RT induced senescence to a much greater level suggesting this mechanism may contribute to radiosensitization (p&lt;0.05). In vivo, combination RT and tamoxifen led to a significant delay in time to tumor doubling (17 days in control, 40 days with tamoxifen alone, 32 days with RT alone, and undefined with combination; p&lt;0.0001) and a significant difference in tumor growth between mice treated with tamoxifen or RT alone compared to mice treated with tamoxifen and RT with synergy noted with combination treatment (FTV 1.297). Conclusion: Our data suggest that ET can radiosensitize ER+ breast tumors, and ET with RT may be more effective for radiosensitization. Ongoing studies will address concurrent versus sequential ET with RT. This work also supports further clinical investigation of the timing of RT for patients receiving ET, especially as ET prior to RT is increasingly used as a bridging therapy during the COVID-19 pandemic.

Citation Format: Anna R Michmerhuizen, Lynn Lerner, Andrea M Pesch, Connor Ward, Rachel Schwartz, Kari Wilder-Romans, Meilan Liu, Bryan Wharram, Alexis Harold, Ruth Azaria, Nicole Zambrana Garcia, Daniel F Hayes, James M Rae, Lori J Pierce, Corey W Speers. Endocrine therapy treatment radiosensitizes estrogen receptor-positive breast cancers [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-02-04.

The impact of chemotherapy on toxicity and cosmetic outcome in patients receiving whole breast irradiation: an analysis within a state-wide quality consortium

PURPOSE

We investigated whether the use of chemotherapy prior to whole breast irradiation (WBI) using either conventional fractionation (CWBI) or hypofractionation (HWBI) is associated with increased toxicity or worse cosmetic outcome compared to WBI alone.

METHODS AND MATERIALS

We identified 6,754 patients who received WBI alone (without a third field covering the superior axillary and supraclavicular nodal regions) with data prospectively collected in a state-wide consortium. We reported rates of four toxicity outcomes: physician-reported acute moist desquamation, patient-reported acute moderate/severe breast pain, a composite acute toxicity measure (including moist desquamation and either patient-reported or physician-reported moderate/significant breast pain), and physician-reported impaired cosmetic outcome at one year following WBI. Successive multivariable models were constructed to estimate the impact of chemotherapy on these outcomes.

RESULTS

Rates of moist desquamation, patient-reported pain, composite acute toxicity, and impaired cosmetic outcome were 23%, 34%, 42%, and 10% for 2,859 patients receiving CWBI and 13%, 28%, 31%, and 11% for 3,895 patients receiving HWBI. Receipt of chemotherapy prior to CWBI was not associated with higher rates of patient-reported pain, composite acute toxicity, or impaired cosmetic outcome compared to CWBI without chemotherapy but was associated with more moist desquamation (OR=1.32 [1.07-1.63], p=0.01). Receipt of chemotherapy prior to HWBI was not associated with higher rates of any of the four toxicity outcomes compared to HWBI alone.

CONCLUSIONS

In this cohort, use of chemotherapy prior to WBI was generally well tolerated. CWBI with chemotherapy, but not to HWBI with chemotherapy, was associated with higher rates of moist desquamation. Rates of acute breast pain and impaired cosmetic outcome at one year were comparable in patients receiving chemotherapy prior to either CWBI or HWBI. These data support the use of HWBI following chemotherapy.

RB expression confers sensitivity to CDK4/6 inhibitor-mediated radiosensitization across breast cancer subtypes

Standard radiation therapy (RT) does not reliably provide locoregional control for women with multinode-positive breast cancer and triple-negative breast cancer (TNBC). We hypothesized that CDK4/6 inhibition (CDK4/6i) would increase the radiosensitivity not only of estrogen receptor–positive (ER⁺) cells, but also of TNBC that expresses retinoblastoma (RB) protein. We found that CDK4/6i radiosensitized RB WT TNBC (n = 4, radiation enhancement ratio [rER]: 1.49–2.22) but failed to radiosensitize RB-null TNBC (n = 3, rER: 0.84–1.00). RB expression predicted response to CDK4/6i + RT (R² = 0.84), and radiosensitization was lost in ER⁺/TNBC cells (rER: 0.88–1.13) after RB1 knockdown in isogenic and nonisogenic models. CDK4/6i suppressed homologous recombination (HR) in RB WT cells but not in RB-null cells or isogenic models of RB1 loss; HR competency was rescued with RB reexpression. Radiosensitization was independent of nonhomologous end joining and the known effects of CDK4/6i on cell cycle arrest. Mechanistically, RB and RAD51 interact in vitro to promote HR repair. CDK4/6i produced RB-dependent radiosensitization in TNBC xenografts but not in isogenic RB1-null xenografts. Our data provide the preclinical rationale for a clinical trial expanding the use of CDK4/6i + RT to difficult-to-control RB-intact breast cancers (including TNBC) and nominate RB status as a predictive biomarker of therapeutic efficacy.

Randomized Phase III Trial Evaluating Radiation Following Surgical Excision for Good-Risk Ductal Carcinoma In Situ: Long-Term Report From NRG Oncology/RTOG 9804

PURPOSE

To our knowledge, NRG/RTOG 9804 is the only randomized trial to assess the impact of whole breast irradiation (radiation therapy [RT]) versus observation (OBS) in women with good-risk ductal carcinoma in situ (DCIS), following lumpectomy. Long-term results focusing on ipsilateral breast recurrence (IBR), the primary outcome, are presented here.

PATIENTS AND METHODS

Eligible patients underwent lumpectomy for DCIS that was mammogram detected, size ≤ 2.5 cm, final margins ≥ 3 mm, and low or intermediate nuclear grade. Consented patients were randomly assigned to RT or OBS. Tamoxifen use was optional. Cumulative incidence was used to estimate IBR, log-rank test and Gray's test to compare treatments, and Fine-Gray regression for hazard ratios (HRs).

RESULTS

A total of six hundred thirty-six women were randomly assigned from 1999 to 2006. Median age was 58 years and mean pathologic DCIS size was 0.60 cm. Intention to use tamoxifen was balanced between arms (69%); however, actual receipt of tamoxifen varied, 58% RT versus 66% OBS (P = .05). At 13.9 years' median follow-up, the 15-year cumulative incidence of IBR was 7.1% (95% CI, 4.0 to 11.5) with RT versus 15.1% (95% CI, 10.8 to 20.2) OBS (P = .0007; HR = 0.36; 95% CI, 0.20 to 0.66); and for invasive LR was 5.4% (95% CI, 2.7 to 9.5) RT versus 9.5% (95% CI, 6.0 to 13.9) OBS (P = .027; HR = 0.44; 95% CI, 0.21 to 0.91). On multivariable analysis, only RT (HR = 0.34; 95% CI, 0.19 to 0.64; P = .0007) and tamoxifen use (HR = 0.45; 95% CI, 0.25 to 0.78; P = .0047) were associated with reduced IBR.

CONCLUSION

RT significantly reduced all and invasive IBR for good-risk DCIS with durable results at 15 years. These results are not an absolute indication for RT but rather should inform shared patient-physician treatment decisions about ipsilateral breast risk reduction in the long term following lumpectomy.

Cardiac Magnetic Resonance Imaging and Blood Biomarkers for Evaluation of Radiation-Induced Cardiotoxicity in Patients With Breast Cancer: Results of a Phase 2 Clinical Trial

PURPOSE

Radiation therapy (RT) can increase the risk of cardiac events in patients with breast cancer (BC), but biomarkers predicting risk for developing RT-induced cardiac disease are currently lacking. We report results from a prospective clinical trial evaluating early magnetic resonance imaging (MRI) and serum biomarker changes as predictors of cardiac injury and risk of subsequent cardiac events after RT for left-sided disease.

METHODS

Women with node-negative and node-positive (N-/+) left-sided BC were enrolled on 2 institutional review board (IRB)-approved protocols at 2 institutions. MRI was conducted pretreatment (within 1 week of starting radiation), at the end of treatment (last day of treatment ±1 week), and 3 months after the last day of treatment (±2 weeks) to quantify left and right ventricular volumes and function, myocardial fibrosis, and edema. Perfusion changes during regadenoson stress perfusion were also assessed on a subset of patients (n = 28). Serum was collected at the same time points. Whole heart and cardiac substructures were contoured using CT and MRI. Models were constructed using baseline cardiac and clinical risk factors. Associations between MRI-measured changes and dose were evaluated.

RESULTS

Among 51 women enrolled, mean heart dose ranged from 0.80 to 4.7 Gy and mean left ventricular (LV) dose from 1.1 to 8.2 Gy, with mean heart dose 2.0 Gy. T1 time, a marker of fibrosis, and right ventricular (RV) ejection fraction (EF) significantly changed with treatment; these were not dose dependent. T2 (marker of edema) and LV EF did not significantly change. No risk factors were associated with baseline global perfusion. Prior receipt of doxorubicin was marginally associated with decreased myocardial perfusion after RT (P = .059), and mean MHD was not associated with perfusion changes. A significant correlation between baseline IL-6 and mean heart dose (MHD) at the end of RT (ρ 0.44, P = .007) and a strong trend between troponin I and MHD at 3 months post-treatment (ρ 0.33, P = .07) were observed. No other significant correlations were identified.

CONCLUSIONS

In this prospective study of women with left-sided breast cancer treated with contemporary treatment planning, cardiac radiation doses were very low relative to historical doses reported by Darby et al. Although we observed significant changes in T1 and RV EF shortly after RT, these changes were not correlated with whole heart or substructure doses. Serum biomarker analysis of cardiac injury demonstrates an interesting trend between markers and MHD that warrants further investigation.

Abstract 1386: The role of MDM2 inhibition in the radiosensitization of ER+ breast cancers

Background​: Radiation therapy (RT) is standard in the treatment of many women with breast cancer (BC). Despite this, women with estrogen receptor positive (ER+) BC respond heterogeneously to RT. Radiosensitization methods for aggressive ER+ disease are needed. We performed a radiosensitizer screen paired with transcriptomic and proteomic data from ER+ models treated +/-RT to identify potential mediators of RT resistance.

Methods​: Clonogenic survival assays were used to determine RT sensitivity of 21 BCC lines as well as radiosensitization with drug treatment. IC50 values were determined for 130 clinical compounds and correlation coefficients were calculated using IC50 values and SF-2Gy. Microarray and RPPA data was used for differential gene/protein expression and pathway analysis. AlamarBlue was used to determine IC-50 values of the MDM2 inhibitor AMG-232. Western blot analysis of Cleaved PARP and Annexin V staining for FLOW was used to measure apoptosis and Cyclins A, E, B and p-Histone H3 and flow cytometry to measure cell cycle progression. yH2AX immunofluorescence was used to measure dsDNA breaks.

Results​: A MDM2 inhibitor (JNJ-26854165) was nominated as an effective drug in treatment for RT-resistant BC cell lines (R2​ = 0.43, p-value &lt;0.01) in our novel radiosensitizer screen. Differential gene expression and pathway analysis in multiple non-overlapping ER+ BC cell lines treated +/-RT identified apoptosis, cell cycle, and p53 signaling as the top pathways induced in ER+ cell lines by RT. Within these MDM2 was significantly overexpressed after RT+ compared to RT- in ER+ p53 wild-type (WT) cells. In p53 mutant (MT) cell lines, however, MDM2 was not differentially expressed. This suggests MDM2 may mediate radioresistance in a p53 dependent manner. Cell growth in the p53​ ​WT cell lines MCF-7 and ZR-75-1 was inhibited by AMG-232, an MDM2 inhibitor (IC-50 values of 554nM and 264nM). p53 MT ER+ cell lines were not sensitive to MDM2 inhibition with this drug (IC-50&gt; 10uM). Clonogenic survival assays demonstrated that at sub-IC50 doses MDM2 inhibition leads to radiosensitization in p53 WT ER+ cell lines (MCF-7 rER: 1.17-2.13; ZR751 rER: 1.30-1.65), however, p53 MT ER+ cells were not radiosensitized (T47D rER: 0.94-1.11; CAMA-1 rER: 0.88-0.95). AMG-232 and RT combined led to an increase in apoptosis compared to RT alone in ER+ p53 WT cells but not p53 MT cells. Combination treatment led to differential cyclin and p-Histone H3 expression in p53 WT cells but not p53 MT cells. ​G1 cell cycle arrest was a secondary effect of MDM2 inhibition and radiation. Experiments investigating the role of dsDNA breaks in radiosensitization are ongoing.

Conclusions​: Our novel radiosensitizer screen identifies MDM2 as a potential mediator of radioresistance in ER+ BC in a p53-dependent manner and suggests that MDM2 targeting concurrent with RT may represent a tractable clinical strategy in women with locally advanced ER+, p53 WT BC.

Citation Format: Cassandra Lynne Ritter, Benjamin C. Chandler, Andrea M. Pesch, Anna R. Michmerhuizen, Nicole Hirsh, Tanner Ward, Amanda Zhang, Mattia Cremona, Lori J. Pierce, Bryan Hennessy, Corey W. Speers. The role of MDM2 inhibition in the radiosensitization of ER+ breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1386.

Abstract 737: Estrogen receptor inhibition with tamoxifen mediates radiosensitization of ER+ breast cancer models

Purpose: Estrogen receptor (ER) expression is present in over 80% of breast tumors and has been shown to be a significant driver of tumor initiation and progression. Therefore, patients with ER-positive (ER+) breast cancers are given first-line therapies which target the ER and downstream ER signaling. Ionizing radiation (RT) has been shown to significantly improve locoregional control and increase overall survival in patients with ER+ breast cancer. Similarly, endocrine therapy (ET) has also been shown to improve metastasis-free and overall survival in women with ER+ breast cancer. While both radiation and ET are used in women with ER+ breast cancer, the effect of endocrine therapies on tumor radiosensitization remains unclear. Here we assessed the efficacy and mechanism of ER inhibition in ER+ breast cancers in combination with radiation therapy.

Methods: Clonogenic survival assays were performed to assess radiosensitization and calculate radiation enhancement ratios (enhR) with the selective estrogen receptor modulator (SERM), tamoxifen, in ER+ MCF-7 and T47D cells or ER-negative (ER-) SUM-159 cells. DNA damage was assessed by yH2AX foci. Efficiency of homologous recombination (HR) or non-homologous end joining (NHEJ) was measured by RAD51 foci or using a pYFP reporter, respectively. Cell cycle effects were measured using flow cytometry with propidium iodide (PI) staining. Apoptosis was assessed by annexin V/PI via flow cytometry. Western blotting was used to quantify expression of proteins and phospho-proteins involved in DNA repair, cell cycle, and apoptosis. An MCF-7 xenograft model was used to assess the efficacy of tamoxifen with RT in vivo.

Results: ER inhibition with tamoxifen radiosensitized ER+ MCF-7 (enhR: 1.14-1.50) and T47D (enhR: 1.33-1.60) cells but not ER- SUM-159 cells (enhR: 0.99-1.02). MCF-7 and T47D cells treated with tamoxifen did not have changes in the kinetics of dsDNA break repair as measured by yH2AX foci (p&gt;0.05) but demonstrated a decrease in NHEJ-mediated repair (p&lt;0.05). No changes were observed in HR-mediated repair by Rad51 foci (p&gt;0.05). While cell cycle arrest was induced at 24 hours after RT, no changes were observed with tamoxifen treatment in combination with RT. In addition, there were no significant changes in apoptosis in MCF-7 or T47D cells with treatment of tamoxifen, radiation, or the combination (p&gt;0.05). In vivo xenograft studies demonstrate a significant delay in time to tumor doubling and a significant difference in tumor growth between mice treated with tamoxifen or RT alone compared to mice treated with tamoxifen and RT.

Conclusion: Our data suggest that tamoxifen may be effectively used to radiosensitize ER+ breast tumors. This work also supports further clinical investigation of the timing of radiation for patients receiving endocrine therapy as concurrent use may be more effective than sequential.

Citation Format: Anna R. Michmerhuizen, Andrea M. Pesch, Rachel Schwartz, Kari Wilder-Romans, Meilan Liu, Ruth Azaria, Alexa Jelley, Lori J. Pierce, Corey W. Speers. Estrogen receptor inhibition with tamoxifen mediates radiosensitization of ER+ breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 737.

Abstract 1952: CDK4/6 inhibition radiosensitizes RB1 wild type triple negative breast cancers through impaired homologous recombination

Purpose: Cyclin-dependent kinase 4&6 (CDK4/6) inhibitors have been approved for the treatment of metastatic, estrogen receptor positive (ER+) breast cancers, but there is growing interesting in CDK4/6 inhibition as a therapeutic strategy in other breast cancer subtypes, including triple negative breast cancer (TNBC). Previous studies have shown that CDK4/6 inhibition radiosensitizes ER+ breast cancers, but the interaction between CDK4/6 inhibition and radiation (RT) in TNBC is incompletely understood.

Methods: Cellular viability was quantified 72 hours after drug treatment (in the absence of RT) to calculate a half maximal inhibitory concentration (IC50) value of proliferation. Radiation enhancement ratios (rER) and surviving fractions of cells after RT were calculated using clonogenic survival assays in RB1 wild type and mutant TNBC cell lines. Homologous recombination (HR) was assessed using RAD51 foci formation and a stable HR reporter system. G1 cell cycle arrest was quantified using propidium iodide-based flow cytometry. CRISPR-induced knockout of RB1 and transient siRNA-mediated knockdown of RB1 in TNBC cell lines was used in both clonogenic survival assays and immunofluorescence experiments. In vivo efficacy of CDK4/6 inhibition + RT was assessed using TNBC patient-derived xenograft models (PDX4664).

Results: Although most TNBC cell lines are resistant to CDK4/6 inhibitor monotherapy (IC50 &gt; 250nM) compared to ER+ cells, treatment with 250nM-1μM palbociclib radiosensitized RB1 wild type TNBC (MDA-MB-231, CAL-51, SUM-159, CAL-120; rER 1.08 – 2.22) but failed to radiosensitize RB1 mutant TNBC (CAL-851, MDA-MB-468; rER: 0.84 – 1.00). Radiosensitization of TNBC cell lines also occurred with short term ribociclib or abemaciclib pretreatment. At 6 and 16 hours following RT, significant suppression of RT-induced homologous recombination (HR) activity (RAD51 foci) was observed in RB1 wild type (p &lt; 0.001) but not RB1 mutant (p &gt; 0.05) TNBC cell lines. Cell cycle arrest after short term CDK4/6 inhibition was dependent on the presence of RB1. In addition, genetic knockdown of RB1 in RB1 wild type TNBC lead to a loss of CDK4/6 inhibitor-mediated HR suppression (p &gt; 0.05) and diminished radiosensitization.

Conclusions: In TNBC, CDK4/6 inhibition and RT leads to suppression of HR activity in an RB1-dependent manner. While ongoing studies seek to elucidate the role of RB1 in HR suppression in the context of CDK4/6 inhibitor-mediated radiosensitization of TNBC, our data suggests that CDK4/6 inhibition + RT could be a valuable clinical strategy to radiosensitize a wide range of breast cancer subtypes, including RB1 wild type TNBC.

Citation Format: Andrea M. Pesch, Nicole Hirsh, Anna R. Michmerhuizen, Benjamin C. Chandler, Kari Wilder-Romans, Meilan Liu, Lori J. Pierce, James M. Rae, Corey W. Speers. CDK4/6 inhibition radiosensitizes RB1 wild type triple negative breast cancers through impaired homologous recombination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1952.

Statewide rates of adjuvant checkpoint inhibitor use after definitive chemoradiation for stage III non-small cell lung cancer

8523

Background: In the landmark PACIFIC trial, adjuvant durvalumab after definitive chemoradiation for unresectable stage III non-small-cell lung cancer (NSCLC) produced a 11% absolute overall survival benefit at two years compared to placebo, and the US Food and Drug Administration approved durvalumab for this indication in February 2018. We investigated the real-world use of adjuvant durvalumab and other immune checkpoint inhibitors (ICI) in a contemporary cohort of patients. Methods: We identified patients with unresectable stage III (AJCC 8th edition) NSCLC treated with definitive chemoradiation from February 2018 to March 2020 from a statewide radiation oncology quality consortium, representing a mix of community (n=22 centers, 336 patients) and academic practice settings (n=5 centers, 64 patients) across the state of Michigan. Use of adjuvant durvalumab or other ICI (atezolizumab, nivolumab, or pembrolizumab) was ascertained at the time of routine three- or six-month follow-up after completion of chemoradiation. Baseline characteristics of patients treated with or without adjuvant ICI were compared with the Chi-squared test for categorical variables and a two-sided t-test for continuous variables. Results: Of 400 patients with unresectable stage III NSCLC treated with definitive chemoradiation, 268 (67%) received adjuvant ICI. Of these, the majority received durvalumab (86%) followed by pembrolizumab (7.5%) and nivolumab (6.0%). The proportion of patients receiving ICI remained stable throughout the study period with no discernable time trends. Eight-five percent of white patients received ICI compared with 77% of black patients (p=0.04), but there were no differences in gender (54.5% male in ICI vs 52.3% no ICI), current smoking (42.2% ICI vs 37.9% no ICI, p=0.68), number of comorbidities (29.5% with 3 or more comorbidities in ICI vs. 26.5% in no ICI, p=0.86), baseline oxygen use (8.9% ICI vs 10.6% no ICI, p=0.59), age (median 66.4 years [IQR 60.3-73.4] for ICI vs. 66.9 years [IQR 61.1-72.2] no ICI, p=0.89), treatment at an academic center (16.0% ICI vs 15.9% no ICI, p=0.97), or ECOG performance status (59.3% ECOG 0 in ICI vs 62.8% no ICI). Conclusions: In a broad range of academic and community-based practices across a state including 27 sites, only two-thirds of potentially eligible stage III NSCLC patients received adjuvant durvalumab or other ICI agents despite a proven overall survival benefit. Receipt of ICI was not strongly associated with baseline demographic or comorbidity variables. Further work will seek to clarify the patient-level reasons behind non-initiation of adjuvant ICI.

Impact of race and socioeconomic status on breast cancer outcomes within the AJCC staging system

e18565

Background: The persistent racial and socioeconomic status (SES) disparities in breast cancer outcomes are partially attributed to propensity towards more aggressive cancers or presentation at higher stages among these groups. Chronic stressors related to race and SES are another major mechanism underlying these inequities. This study aims to examine the effect of race and SES within the AJCC 8th-edition staging system, which incorporates anatomic extent of disease and tumor biology. Methods: The SEER breast cancer database linked with county-level census data was used to identify patients with invasive breast cancer from 2010-2015. The database includes a composite SES-index which was analyzed in quintiles. Cox proportional-hazards regression was used to estimate disease-specific survival (DSS). Results: 259,852 patients were included: 176,369 (67.9%) non-Hispanic white, 28,510 (11.0%) Black, 29,737 (11.4%) Hispanic, and 22,887 (8.8%) Asian. Black race, lower SES, public insurance, lower education, and increased poverty were associated with decreased DSS. Adjusted survival analysis for patient, SES, tumor, and treatment characteristics demonstrated that patients of black race had inferior DSS within each stage. Fully adjusted models also showed patients residing in lower SES counties had inferior DSS [Table]. Conclusions: Racial and SES disparities in breast cancer-specific mortality were evident across all stages of disease. Future efforts to improve breast cancer outcomes should systematically assess and address racial and socioeconomic factors as fundamental drivers of inequitable outcomes.

Adjusted 5-year DSS Estimates, Stratified by Race and SES.[Table: see text]

Discovery and validation of a genomic signature to identify women with early-stage invasive breast cancer who may safely omit adjuvant radiotherapy after breast-conserving surgery

512

Background: Adjuvant radiotherapy (RT) is currently the standard of care for women with early-stage invasive breast cancer (BC) treated with breast conserving surgery (BCS). However, some women may have very low risk of recurrence and could safely be spared RT. This study aimed to identify these women using a molecularly-based approach. Methods: We performed an analysis of the SweBCG91-RT cohort, a trial randomizing women with node-negative stage I-II invasive BC +/- RT following breast conserving surgery, with sparse use of adjuvant systemic therapy. Only patients with ER+, HER2- tumors, and not treated with adjuvant systemic therapy, were included in this analysis. Transcriptome-wide profiling of tumors was performed using the Affymetrix Human Exon 1.0 ST microarray. The SweBCG91-RT cohort was divided into a training cohort of 243 patients and a validation cohort of 354 patients. Biological gene sets and individual genes related to locoregional recurrence in patients not receiving RT of the training set were identified, and a 16-gene signature was trained using elastic net regression. The signature, named Profile for the Omission of Local Adjuvant Radiation (POLAR), was locked prior to validation. Results: In the validation cohort, POLAR was prognostic for locoregional recurrence (LRR) in patients not treated with RT (multivariable Cox model adjusting for age, grade, tumor size, and luminal A vs luminal B: HR = 1.7 [1.2,2.3], p < 0.001). Patients categorized as POLAR low-risk had a 10-year locoregional recurrence rate of 7% in the absence of RT. Notably, there was no significant benefit from RT for these POLAR low-risk patients (HR = 1.1 [0.38,3.3], p = 0.83), whereas patients categorized as POLAR high-risk had a significant decreased risk of locoregional recurrence when treated with RT (recurrence rate without RT at 10-years 19%, HR = 0.43 [0.24,0.78], p = 0.0053). Conclusions: These data suggest that the novel POLAR genomic signature based on LRR biology can not only identify patients who have a low risk of LRR without adjuvant RT after BCS but who also would not benefit from RT, thus being prime candidates for RT omission.

Attention to diet, exercise, and weight in the oncology clinic: Results of a national patient survey

10549

Background: Obesity and related factors are increasingly associated with increased risk of developing and dying from cancer. The American Society of Clinical Oncology (ASCO) conducted a survey of cancer patients to assess their experience in receiving recommendations and referrals related to weight, diet and exercise as a part of their cancer care. Methods: An online survey was distributed to potential participants between March and June 2020 via ASCO channels and patient advocacy organizations, with an estimated reach of over 25,000 individuals. Eligibility criteria included being 18 years, living in the US, and having been diagnosed with cancer. Logistic regression was used to determine factors associated with recommendation and referral patterns. Results: In total, 2419 individuals responded to the survey. Most respondents were female (75.5%), 61.8% had an early-stage malignancy, 38.2% had advanced disease, and 49.0% were currently receiving treatment. Breast cancer was the most common cancer type (36.0%). Average BMI was 25.8 kg/m2. The majority of respondents consumed £2 servings of fruits and vegetables per day (50.9%) and exercised £2 times per week (50.4%). Exercise was addressed at most or some oncology visits in 57.5% of respondents, diet in 50.7%, and weight in 28.4%. Referrals were less common: 14.9% of respondents were referred to an exercise program, 25.6% to a dietitian and 4.5% to a weight management program. In multiple regression analyses, racial and ethnicity minority respondents were more likely to receive advice about diet (Odds Ratio [OR] 1.92, 95% CI 1.56-2.38) and weight (OR 1.64, 95% CI 1.23-2.17) compared to non-Hispanic whites, individuals diagnosed with cancer in the past 5 yrs (vs > 5 yrs) were more likely to receive advice about exercise (OR 1.48, 95% CI 1.23-1.79), and breast cancer patients were more likely to receive advice about exercise (OR 1.37, 95% CI 1.11-1.68) and weight (OR 1.46, 95% CI 1.03-2.07) than other cancer patients. Overall, 74% of survey respondents had changed their diet or exercise after cancer diagnosis. Respondents reporting that their oncologist spoke to them about increasing exercise or eating healthier foods were more likely to report a change in behavior than those whose oncologists did not (exercise: 79.6% vs 69.0%, P < 0.001; diet 81.1% vs 71.4%, P < 0.001). Respondents whose oncologist had spoken to them about exercise were more likely to exercise > 2 times per week compared to respondents whose oncologists did not address exercise (53.5% vs 44.1%, P < 0.001). Conclusions: In a national survey of oncology patients, slightly more than half of respondents reported attention to diet and exercise during oncology visits. Provider recommendations for diet and exercise were associated with positive changes in these behaviors. Additional attention to diet and exercise as part of oncology visits is needed to help support healthy lifestyle change in cancer patients.

NCCN Guidelines® Insights: Breast Cancer, Version 4.2021

The NCCN Guidelines for Breast Cancer include up-to-date guidelines for clinical management of patients with carcinoma in situ, invasive breast cancer, Paget disease, phyllodes tumor, inflammatory breast cancer, male breast cancer, and breast cancer during pregnancy. These guidelines are developed by a multidisciplinary panel of representatives from NCCN Member Institutions with breast cancer-focused expertise in the fields of medical oncology, surgical oncology, radiation oncology, pathology, reconstructive surgery, and patient advocacy. These NCCN Guidelines Insights focus on the most recent updates to recommendations for adjuvant systemic therapy in patients with nonmetastatic, early-stage, hormone receptor-positive, HER2-negative breast cancer.

Abstract PO-028: RB loss mitigates CDK4/6 inhibitor-mediated radiosensitization of estrogen receptor positive (ER+) breast cancers

Purpose: Fractionated radiation (RT) is used in the adjuvant setting for locoregional control and to prevent the development of metastatic lesions in estrogen receptor positive (ER+) breast cancers. We previously demonstrated that inhibition of cyclin-dependent kinases 4 and 6 (CDK4/6) along with RT leads to the radiosensitization of ER+ breast cancers, but the exact mechanism by which this occurs is unknown. We hypothesized that the presence of RB is necessary for effective double strand repair of radiation-induced DNA damage mediated through homologous recombination (HR), and that this is prevented using CDK4/6 inhibition. Methods: Pharmacological CDK4/6 inhibition was achieved using three FDA approved CKD4/6 inhibitors: palbociclib, ribociclib, and abemaciclib. Genetic knockdown of RB1 was performed using siRNA and knockout was achieved using a CRISPR-Cas9 system. Parental and RB1 knockdown/CRISPR MCF-7 and T47D cells were treated for 72 hours to assess drug sensitivity. Cells were pretreated with a CDK4/6 inhibitor one hour prior to RT and colony formation was quantified to assess changes in radiosensitivity. MCF-7 cells expressing an HR-specific GFP reporter were used to assess HR competency. RB, yH2AX, and RAD51 cellular localization following RT and CDK4/6 inhibition was assessed using immunofluorescence assays. Flow cytometry with propidium iodide staining was used to assess cell cycle distribution. Protein expression was assessed by immunoblotting. Results: CDK4/6 inhibition with palbociclib, ribociclib, and abemaciclib + RT radiosensitizes ER+ breast cancer cells at sub-IC50 concentrations in vitro (rER: 1.21 – 2.05) through impaired HR, which we confirmed using MCF-7 cells that express a stable HR-GFP reporter system (p &lt; 0.01). RB1 knockdown decreased single-agent efficacy of CDK4/6 inhibition on the proliferation of ER+ breast cancer cell lines, leading to an increase in the IC50 for each CDK4/6 inhibitor. Palbociclib, ribociclib, and abemaciclib failed to induce G1 cell cycle accumulation after RB1 knockdown (p &gt; 0.05). Genetic knockdown of RB1 led to a decrease in the ability of breast cancer cells to perform HR-directed DNA repair (p &lt; 0.01) independent of drug treatment, and further suppression of HR with CDK4/6 inhibition was lost in MCF-7 and T47D cells lacking RB expression (p &gt; 0.05). Furthermore, RB protein is necessary for CDK4/6i mediated radiosensitization as evidenced by the abrogation of radiosensitization in RB null isogenic models of ER+ breast cancer (MCF-7 rER: 0.97 ± 0.13). Conclusions: Our data suggests that CDK4/6 inhibitor-mediated radiosensitization and HR suppression is dependent on RB expression. Thus, RB might serve as an effective biomarker for patient selection in future clinical trials that seek to combine CDK4/6 inhibition + RT.

Citation Format: Andrea M. Pesch, Nicole Hirsh, Anna R. Michmerhuizen, Benjamin C. Chandler, Kari Wilder-Romans, Meilan Liu, Erin Cobain, Lori J. Pierce, James M. Rae, Corey Speers. RB loss mitigates CDK4/6 inhibitor-mediated radiosensitization of estrogen receptor positive (ER+) breast cancers [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-028.