Mechanisms of Intrinsic Radioresistance in Breast Cancer Identify Potential Therapeutic Vulnerabilities

PURPOSE/OBJECTIVE(S)

Clinical management of breast cancer (BC) includes radiation therapy (RT) for most women, though the molecular mechanisms that underly RT response and intrinsic radioresistance are poorly understood. Both in vitro and in vivo models aid in our understanding of radiobiology, and we hypothesized that transcriptional changes caused by radiation in vitro in BC cell lines would be recapitulated in an in vivo mouse xenograft model and uncover targetable mechanisms of radioresistance in BC.

MATERIALS/METHODS

Radiosensitivity was measured with clonogenic survival assays in 16 cell lines. RNA-seq experiments in vitro and in vivo were performed in an RT resistant (SUM-159) and RT sensitive (ZR-75) cell line 24 hrs after 4 Gy or after 2 Gy x 6 fractions, respectively. Differentially expressed genes (DEGs) were identified from RNA-seq data with DeSeq2 followed by pathway analysis with iPathwayGuide.

RESULTS

RT sensitivity was subtype independent in 16 BC cell lines, with SUM-159 radioresistant (SF 0.88) and ZR-75-1 radiosensitive (SF 0.29). There were 75 unique pathways that were significantly altered after RT in SUM-159 cells (53 pathways in vivo only, 36 pathways in vitro only, 14 both conditions; adjusted p-value < 0.05) and 85 unique pathways that were significantly altered after RT in ZR-75-1 cells (16 pathways in vivo only, 72 in vivo only, 3 both conditions; adjusted p-value < 0.05). Pathways that were significantly affected in both cell lines exclusively in the in vitro condition include canonical RT response pathways such as cell cycle, cellular senescence, and DNA replication, though the direction of DEGs were opposite in the two cell lines for each of these pathways. The IL-17 signaling pathway was significantly altered for both cell lines in vivo. Of the pathways that were significantly altered in both conditions for SUM-159 cells, inflammation, including chemokine signaling pathway and cytokine-cytokine receptor interaction, were among the most significant. Significantly more cytokines were upregulated following RT in vivo than in vitro. Cytokines were not upregulated in ZR-75-1 cells in vitro or in vivo.

CONCLUSION

Taken together, the significant changes in the IL-17 pathway and the upregulation of cytokines only in vivo indicate a potential of the tumor microenvironment in the in vivo condition that the in vitro condition lacks. Increased heterogeneity in vivo relative to in vitro may also explain the absence of several canonical RT response pathways in the in vivo conditions for each cell line. Notably, the opposite direction of DEG changes in the canonical RT response pathways between the 2 cell lines with disparate radiosensitivity levels may point to important biologic vulnerabilities that may be targeted in the resistant SUM-159 cells. Future studies are underway using additional BC cell lines and single-cell analysis to better understand RT response heterogeneity.

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.

Disparities in Acute Radiation-Related Pain and Dermatitis between Black and White Patients with Early-Stage Breast Cancer Receiving Adjuvant Radiation Following Breast Conserving Surgery

PURPOSE/OBJECTIVE(S)

Historically, black patients with cancer experience poor clinical outcomes and low quality of life due to inadequate screening and management of cancer-related treatment toxicities. There are limited data documenting racial disparities in acute radiation-related toxicities (ARRTs) for patients with early-stage breast cancer. Therefore, we compared ARRTs between Black (B) and White (W) patients receiving adjuvant radiation following breast conserving surgery (BCS).

MATERIALS/METHODS

This retrospective analysis included 317 patients with stage 0/1 breast cancer treated with adjuvant radiation between October 2019 and February 2022. 29% (N = 81) were B and 71% (N = 236) were W, with an average age of 65 (range: 32-88) for both. We abstracted weekly on-treatment-visit clinical notes (OTVs) completed by a nurse and radiation oncologist who utilized the Common Terminology Criteria for Adverse (CTCAE) v4.0 to evaluate each patient's pain score (scaled 0-10, 0 = no pain and 10 = worst), radiation dermatitis (RD; Grade 0-4), as well as non-CTCAE descriptors of pain and presence of hyperpigmentation or pruritus. We compared onset and severity of pain and rates of RD and pruritus between B and W patients.

RESULTS

The proportion reporting pain was significantly lower among B vs. W patients (43.8% vs. 63.6%; P = 0.002). Of patients qualitatively reporting pain, B patients were significantly more likely to have their pain scored as 0 than W patients (24.3% vs. 11.7%; P = 0.024). B patients had significantly lower median pain scores than W patients (P = 0.010), with a median score of 3 (interquartile range [IQR]: 0-5.5) vs. 5 (IQR: 4-8). B patients had a significantly longer time to pain identification than W patients (P = 0.027), with median time to pain of 10th fraction (IQR: 4-13.5) vs. 8th fraction (IQR: 4-11). Radiation dermatitis was graded as 0 (50.6% vs 8.5%; P<0.001), 1 (44.4% vs 82.6%; P<0.001), 2 (14.8% vs 15.3%, P = NS), and 3 (3.7% vs 0.4%; P = 0.023), with no grade 4 RD, amongst B and W patients, respectively. Of note, B patients experiencing mild hyperpigmentation were graded as 0. We found no statistically significant differences in incidence of pruritus.

CONCLUSION

Qualitative and quantitative analyses of ARRTs based on CTCAE v4.0 show discordance in pain scores and radiation dermatitis. The underscoring of pain amongst B patients suggests possible cultural hesitancy to report pain or implicit biases in evaluating pain suggesting the need for alternative ways to discuss and score pain in B patients. Our data suggests that CTCAE does not effectively assess radiation dermatitis in B patients. There are no descriptors of hyperpigmentation in grading of radiation dermatitis in CTCAE, which may lead to underreporting in dark-skinned individuals. Better assessment tools are needed to document ARRTs to ensure appropriate evaluation and treatment across all racial groups.

Sequence of therapy and survival in patients with advanced pancreatic neuroendocrine tumours

Background

Pancreatic neuroendocrine tumours (pnets) often present as advanced disease. The optimal sequence of therapy is unknown.

Methods

Sequential patients with advanced pnets referred to BC Cancer between 2000 and 2013 who received 1 or more treatment modalities were reviewed, and treatment patterns, progression-free survival (pfs), and overall survival (os) were characterized. Systemic treatments included chemotherapy, small-molecule therapy, and peptide receptor radionuclide therapy.

Results

In 66 cases of advanced pnets, median patient age was 61.2 years (25%-75% interquartile range: 50.8-66.2 years), and men constituted 47% of the group. First-line therapies were surgery (36%), chemotherapy (33%), and somatostatin analogues (32%). Compared with first-line systemic therapy, surgery in the first line was associated with increased pfs and os (20.6 months vs. 6.3 months and 100.3 months vs. 30.5 months respectively, p < 0.05). In 42 patients (64%) who received more than 1 line of therapy, no difference in os or pfs between second-line therapies was observed.

Conclusions

Our results confirm the primary role of surgery for advanced pnets. New systemic treatments will further increase options.

Abstract ES2-2: Evolving opportunities to personalize radiation decisions - Guiding decisions to omit radiation after breast conserving surgery for invasive breast cancer

Much as the development of molecularly based signatures (OncotypeDx®, MammaPrint®, ProSigna™, etc.) has revolutionized the decision-making process surrounding the need for adjuvant chemotherapy in women with early stage breast cancer, the development of prognostic and predictive signatures to determine the need and efficacy of radiation for women with breast cancer holds similar promise. While preliminary efforts to develop these signatures has been encouraging, much work remains in order to successfully translate these signatures into the clinic. In this educational session, we will review the current status of genomic-based signatures for radiation decision making. We will also review the barriers to clinical adoption and the molecularly stratified trials testing these signatures for treatment omission. Ultimately, for any of these tests to be translated into the clinic it will require demonstration of their accuracy and reproducibility as a test and perhaps more importantly, demonstration of clinical utility and an ability to improve outcomes for women with breast cancer. While not yet realized, the ongoing development of these signatures holds much promise as the field seeks to finally realize “personalized medicine” as it relates to radiation treatment for women with breast cancer.

Citation Format: C Speers. Evolving opportunities to personalize radiation decisions - Guiding decisions to omit radiation after breast conserving surgery for invasive breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr ES2-2.

In the Era After the European Organisation for Research and Treatment of Cancer 'Boost' Study, is the Additional Radiotherapy to the Breast Tumour Bed Still Beneficial for Young Women?

AIMS

The European Organisation for Research and Treatment of Cancer (EORTC) 22,881-10,882 trial showed significant benefit of a radiotherapy boost (RTB) in women ≤40 years in a pre-hormone therapy (HT) era. We determined how the use of HT and RTB changed in response to clinical guidelines and whether the benefit of routine RTB was still observed in the HT era.

MATERIALS AND METHODS

Between 1996 and 2004, a provincial database identified all women ≤40 years with breast cancer who met the inclusion criteria of the EORTC trial. In total, 411 patients were classified into three eras defined by the guidelines: era 1 (discretionary HT, discretionary RTB); era 2 (routine HT, discretionary RTB); era 3 (routine HT, routine RTB). HT use, RTB use and cumulative incidence of local recurrence were calculated and compared across eras.

RESULTS

HT use increased after the first policy change from 13% to 75% for oestrogen receptor-positive patients (P < 0.01). RTB use also increased from 33% to 76% following the second policy change (P < 0.01). At 10 years, the cumulative incidence of local recurrence was 12% in era 1, 6% in era 2 and 6% in era 3 (era 2 versus era 3, P = 0.92). For patients in the routine HT era (eras 2 and 3 combined) there was no significant difference in local recurrence between RTB and 'no RTB' patients (6% versus 7%, P = 0.81).

CONCLUSIONS

The routine use of HT and RTB increased significantly after new practice guidelines. Introduction of the HT guideline was associated with a 6% improvement in local recurrence at 10 years. No improvement in local recurrence was associated with the introduction of the RTB guideline in the HT era. The routine use of a boost in unselected young women with negative margins should be re-evaluated in the current HT era.

Abstract P5-12-01: A novel gene expression signature prognostic for both locoregional and distant failure and predictive for adjuvant radiotherapy

Background: Most patients with early stage breast cancer (BC) are treated with adjuvant radiotherapy (RT) following breast conserving surgery (BCS) to prevent locoregional recurrences (LRR). No predictive tools are currently available to select patients for RT, resulting in considerable over- and under treatment. We aimed to create and validate a gene expression-based classifier to prognosticate for LRR and to stratify patients for treatment with RT.

Patients and methods: A 27-gene expression signature was developed using three publicly available early stage BC gene expression datasets where patients were treated with RT and had detailed local recurrence information. The largest of the datasets was used to train the signature, and the other two datasets were used for signature refinement. As age was the strongest clinical factor for the endpoint in the training dataset, it was included in the model, resulting in a final clinical-genomic classifier of 27 genes and age. The classifier was locked before external validation in the SweBCG91-RT trial. This phase III clinical trial included primary tumors from 765 patients and for which gene expression data was available. The trial randomized node-negative BC patients to +/- RT following BCS, with sparse use of adjuvant systemic treatment (9%) and a median follow-up of 14.0 years for LRR in patients free from event. The classifier was validated using Cox regression with LRR as the primary endpoint, and hazard ratios (HRs) were calculated using the raw continuous classifier score (range: 0.5 to 2.5).

Results: The novel classifier was highly prognostic for LRR in SweBCG91-RT patients treated with RT (HR=7.5[3.3-16.9], p&lt;0.001), and remained prognostic in multivariate analysis (MVA) that included systemic treatment, subtype and grade (HR=7.2[3.1-16.4], p&lt;0.001). To a lesser extent, the classifier was also prognostic for LRR in patients not treated with RT (HR=1.9[1.0-3.5], p=0.03; MVA HR=1.9[1.0-3.3], p=0.05). Patients at high risk of LRR had a smaller effect of RT, and the treatment predictive potential was confirmed by testing for interaction (pinteraction=0.008). In patients treated with RT, age and the genomic component of the model were both prognostic for LRR (p&lt;0.01) as well as predictive for RT response (pinteraction&lt;0.05) and provided independent information (p&lt;0.01). The combined classifier has increased performance over its individual components (10-year AUC=0.72, 0.67, 0.65 for the classifier, age, and genomic component, respectively). While the novel signature was prognostic for metastasis (HR=4.3[2.3-7.8], p&lt;0.0001), calculated scores from previously published signatures to the metastasis endpoint, including the Oncotype-like score, were not prognostic for LRR.

Conclusions: This novel gene expression signature is highly prognostic for LRR, can identify patients at risk of LRR despite RT, and appears to be treatment predictive for adjuvant RT. Furthermore, the current signature is highly prognostic for metastasis. In contrast, calculated scores of previously published signatures modeled for the metastasis endpoint had inferior performance for LRR. These results underscore both the importance of signatures prognostic for LRR and the similarities in the biology of LRR and distant failure.

Citation Format: Sjöström M, Chang SL, Fishbane N, Davicioni E, Zhao SG, Hartman L, Holmberg E, Feng FY, Speers CW, Pierce LJ, Malmström P, Fernö M, Karlsson P. A novel gene expression signature prognostic for both locoregional and distant failure and predictive for adjuvant radiotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-12-01.

Abstract P4-08-27: The 21-gene Recurrence® (RS) Score assay in estrogen receptor positive node negative breast cancer: Real-world chemotherapy usage and patient characteristics within the intermediate and high-risk RS category

Background:

The Oncotype Dx, a 21-gene recurrence score (RS) assay, has been validated as a prognostic tool in early-stage, hormone receptor-positive, HER2-negative breast cancer. A RS of ≥ 31 is predictive for chemotherapy benefit. However, it has not been clearly established whether more intensive chemotherapy regimens for these patients provide further benefit and whether higher RS stratifications (≥41) influence treatment decisions.

Methods:

From the prospective British Columbia (BC) Breast Cancer Outcomes Unit database, we identified patients with N0 disease who received Oncotype Dx testing from May 2010 to December 2016. Patients with previous or synchronous breast cancer, and patients treated with neoadjuvant chemotherapy were excluded. Groups were defined that had an Oncotype Dx RS of 31-40 and ≥ 41. Demographic characteristics and type of chemotherapy received were collected. Additional subgroups were defined for patients who had a RS of 21-25 and who were ≤ 50 years old and &gt; 50 years old.

Results:

We identified 1,202 patients who received Oncotype Dx testing over the time period studied, with 14.8% (n=178) having a RS of ≥ 31. Among these high-risk patients, the median age was 58 (range 34-79), 90% received hormonal therapy and 85% received chemotherapy. In this cohort, 46% received docetaxel and cyclophosphamide for 4 cycles and 28% received 3rd generation chemotherapy. The use of 3rd generation chemotherapy in patients with a RS of ≥ 41 was significantly higher than in patients with RS between 31-40 (39% vs 22%, p = 0.006). Among patients who had a RS of 21-25 and who were ≤ 50 years old (n = 49), 53% received chemotherapy. Of patients who had a RS of 21-25 and who were &gt; 50 years old (n = 127), 16% received chemotherapy.

Conclusions:

Among patients with a RS ≥ 31, decisions regarding chemotherapy usage were heterogeneous with docetaxel and cyclophosphamide for 4 cycles being the most commonly used regimen. However, in those with a RS ≥ 41, 3rd generation chemotherapy was preferred. Patients with a RS between 21-25 and who were ≤ 50 years old received more chemotherapy than patients who were &gt; 50 years old.

 RS 31-40 (n=116)RS ≥ 41 (n=62)RS ≥ 31 (n=178)Median age58.0 (range, 36-79)57.5 (range 34-78)58.0 (range 34-79)Pre-menopausal28.4%29.0%28.7%Hormonal therapy93.1%83.9%89.9%Chemotherapy86.2%82.3%84.8%DCx4 (1)54.3% (n=63/116) Median age 59.0 (range, 36 – 78)30.6% (n=19/62) Median age 64.0 (range, 42 – 78)46.1% (n=82/178) Median age 59.5 (range, 36 – 78)3rd generation chemo (2)21.6% (n=25/116) Median age 56.0 (range, 39 – 79)38.7% (n=24/62) Median age 52.0 (range, 34 – 76)27.5% (n=49/178) Median age 54.0 (range, 34 – 79)Other chemo10.3% (n=12/116) Median age 57.5 (range, 52 – 78)12.9% (n=8/62) Median age 64.0 (range, 42 – 72)11.2% (n=20/178) Median age 58.5 (range, 42 – 78)(1) Docetaxel and cyclophosphamide, 4 cycles (2) Anthracycline and Taxane containing regimens, 6 cycles or 8 cycles

Citation Format: Le D, Chia S, Simmons C, Speers C, Gondara L, Nichol A, Lohrisch C, Gelmon KA. The 21-gene Recurrence® (RS) Score assay in estrogen receptor positive node negative breast cancer: Real-world chemotherapy usage and patient characteristics within the intermediate and high-risk RS category [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-27.

Abstract P4-08-03: Looking forward to the TNM 9th edition: Is it time to stage the different breast cancer subtypes as distinct diseases?

Background: For clinical purposes, four subtypes of breast cancer: Luminal A (LumA), Luminal B (LumB), Her2-positive (H2P) and Triple-Negative (TN) are commonly recognized. This study investigated staging them independently as different diseases. The hypothesis was that the anatomic staging system of the 8th TNM edition would have good prognostic performance within each breast cancer subtype, as defined by estrogen receptor (ER), progesterone receptor (PR), Her2 amplification (H2) and grade.

Methods: Using the Breast Cancer Outcomes Unit database, we identified patients treated without neoadjuvant therapy between 2005 and 2009, when use of anti-Her2 therapy (AH2T) was routine for H2+ disease. We approximated the four subtypes of breast cancer described in Table 48.2 of the revised January 25, 2018 version of the TNM 8th edition (https://cancerstaging.org/references-tools/deskreferences/Pages/Breast-Cancer-Staging.aspx) as follows: LumA ER3+ AND PR3+ AND H2- AND (G1-2); LumB All Non-LumA (ER+ OR PR+) AND H2-; H2P All H2+; and TN ER- AND PR- AND H2-. Breast cancer-specific survival (BCSS) was determined for anatomic stages I-IV within each subtype by the Kaplan-Meier method. The predominant usage of hormone therapy (HT), chemotherapy (ChT) and AH2T was compared by subtype for patients &lt; 70 years, who were generally eligible for ChT.

Results: The median follow-up for the 8,640 patients was 10.0 years. The numbers of patients within each subtype were: LumA = 2,288, LumB = 4,097, H2P = 1,374, and TN = 881. The predominant systemic therapies used by subtype were: LumA: HT = 60.2% and HT+ChT = 29.8%; LumB: HT = 45.9% and HT+ChT = 42.1%; H2P: HT+ChT+AH2 = 40.1% and ChT+AH2 = 35.0%; and TN: ChT = 79.1%. The confidence intervals for BCSS in stages I, II, III, and IV were distinct for the four subtypes, as shown in Table 1.

BCSS by Stage for Clinical Breast Cancer Subtypes1-year BCSSLumA (%) (CI)LumB (%) (CI)H2P (%) (CI)TN (%) (CI)Stage I98.1 (97.0, 98.8)96.5 (95.5, 97.2)95.4 (92.9, 97.0)90.4 (86.5, 93.2)Stage II93.4 (91.1, 95.1)86.5 (84.6, 88.3)87.2 (84.1, 89.7)81.4 (77.3, 84.9)Stage III79.9 (71.8, 85.9)66.1 (61.5, 70.3)74.0 (68.1, 78.9)58.0 (48.3, 66.5)Stage IV42.9 (17.7, 66.0)16.9 (8.1, 28.6)33.1 (18.6, 48.3)0.0 (0.0, 0.0)

Conclusions: The anatomic staging system provided reliable BCSS prognostication within breast cancer subtypes. Individualizing treatment using anatomic staging within breast cancer subtypes, would permit decisions about the volume of radiotherapy and the need for intensification of systemic therapy to be made using the familiar and time-tested risk metric of disease extent. In the future, as breast cancer subtyping becomes more sophisticated, prognostication using anatomic staging within these distinct diseases should become increasingly accurate.

Citation Format: Nichol AM, Lohrisch CA, Gondara L, Speers C, Gelmon KA. Looking forward to the TNM 9th edition: Is it time to stage the different breast cancer subtypes as distinct diseases? [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-03.

Prescribing practices of endocrine therapy for ductal carcinoma in situ in British Columbia

Purpose

The mainstay of treatment for ductal carcinoma in situ (dcis) involves surgery in the form of mastectomy or lumpectomy. Inconsistency in the use of endocrine therapy (et) for dcis is evident worldwide. We sought to assess the variation in et prescribing for patients with dcis across a population-based radiotherapy (rt) program and to identify variables that predict its use.

Methods

Data from a breast cancer database were obtained for women diagnosed with dcis in British Columbia from 2009 to 2014. Associations between et use and patient characteristics were assessed by chi-square test and multilevel multivariate logistic regression. The Kaplan-Meier method, with propensity score matching and Cox regression analysis, was used to assess the effects of et on overall survival (os) and relapse-free survival (rfs).

Results

For the 2336 dcis patients included in the study, et use was 13% in dcis patients overall, and 17% in patients with estrogen receptor-positive (er+) tumours treated with breast-conserving surgery and rt. Significant variation in et use by treatment centre was observed (range: 8%-23%; p < 0.001), and prescription of et by individual oncologists varied in the range 0%-40%. After controlling for confounding factors, age less than 50 years [odds ratio (or): 1.72; p = 0.01], treatment centre, er+ status (or: 5.33; p < 0.001), and rt use (or: 1.77; p < 0.001) were significant predictors of et use. No difference in os or rfs with the use of et was observed.

Conclusions

In this population-based analysis, 13% of patients with dcis in British Columbia received et, with variation by treatment centre (8%-23%) and individual oncologist (0%-40%). Age less than 50 years, er+ status, and rt use were most associated with et use.

Factors affecting radiotherapy prescribing patterns in the post-mastectomy setting

Background

Radiation therapy (rt) after mastectomy for breast cancer can improve survival outcomes, but has been associated with inferior cosmesis after breast reconstruction. In the literature, rt dose and fractionation schedules are inconsistently reported. We sought to determine the pattern of rt prescribing practices in a provincial rt program for patients treated with mastectomy and reconstruction.

Methods

Women diagnosed with stages 0-iii breast cancer between January 2012 and December 2013 and treated with curative-intent rt were identified from a clinicopathology database. Patient demographic, tumour, and treatment information were extracted. Of the identified patients, those undergoing mastectomy were the focus of the present analysis.

Results

Of 4016 patients identified, 1143 (28%) underwent mastectomy. The patients treated with mastectomy had a median age of 57 years, and 37% of them underwent reconstruction. Treatment with more than 16 fractions of rt was associated with autologous reconstruction [odds ratio (or): 37.2; 95% confidence interval (ci): 11.2 to 123.7; p < 0.001], implant reconstruction (or: 93.3; 95% ci: 45.3 to 192.2; p < 0.001), and treating centre. Hypofractionated treatment was associated with older age (or: 0.94; 95% ci: 0.92 to 0.96; p < 0.001), and living more than 400 km from a treatment centre (or: 0.37; 95% ci: 0.16 to 0.86; p = 0.02).

Conclusions

Prescribing practices in breast cancer patients undergoing mastectomy are influenced by reconstruction intent, age, nodal status, and distance from the treatment centre. Those factors should be considered when making treatment decisions.

Abstract P1-09-05: Radiosensitization of androgen receptor (AR)-positive triple-negative breast cancer (TNBC) cells using seviteronel (INO-464), a selective CYP17 lyase and AR inhibitor

Background: Increased rates of locoregional recurrence (LR) have been observed in TNBC despite chemotherapy and radiation (RT). A novel radiosensitizer screen nominated the AR as a promising target for treatment of radioresistant breast cancer, including TNBC. We assessed the activity of seviteronel (Sevi), a selective CYP17 lyase and AR inhibitor in Phase 2 clinical development for advanced breast and prostate cancer, as a potential radiosensitizer in AR+ TNBC model.

Methods: Clonogenic survival assays were used to determine the intrinsic RT sensitivity of 21 breast cancer cell (BCC) lines. IC50 values were determined for 130 clinically available compounds and correlation coefficients were calculated using IC50 values and SF-2Gy. Gene expression was measured using RNA Seq or qRT-PCR and protein expression was measured using RPPA arrays. AR function was assessed using functional inhibition with Sevi in MDA-MB-453, ACC-422, ACC-460, SUM-185 (all four AR+ TNBC), MDA-MB-231 (AR- TNBC), and T47D (AR- ER+) BCC lines. Double-stranded DNA (dsDNA) break repair was assessed with γH2AX foci counting. In vivo tumor growth was measured with varying control and treatment groups (16-20 tumors/group). Kaplan-Meier analysis was performed to estimate local control. A Cox proportional hazards model and multi-variate analysis (MVA) were used to determine variables associated with LRF survival.

Results: Our novel radiosensitizer screen identified the activity of anti-androgen therapy as a potentially effective strategy for radiosensitization in RT-resistant BCC lines (R2 =0.46, p-value &lt; 0.01) (Speers et al, J Clin Oncol 35, 2017 (suppl; abstr e12102). Heterogeneity in AR expression was identified in human BCC lines and TNBC samples from patients (N=2098). There was a strong correlation between AR RNA expression and protein expression across all BC intrinsic subtypes. AR inhibition using Sevi induced radiation sensitivity in vitro with an enhancement ratio (ER) of 1.24-1.69 in four different AR+ TNBC lines. No such radiosensitization was seen in AR(-) TNBC or ER+, AR(-) BCC lines. Radiosensitization was at least partially dependent on impaired dsDNA break repair with significant delays in dsDNA break repair at 16 and 24 hours in all AR+ TNBC lines examined (p-value &lt; 0.01). AR inhibition with Sevi significantly radiosensitized AR+ TNBC xenografts in mouse models and markedly delayed tumor-volume tripling time (TTT) and tumor growth (MDA-MB-453: median TTT 16.1 days for RT alone vs. not reached after 45 days for Sevi+RT, p-value &lt;0.001). Similar delays were seen in tumor growth, weight, and tumor doubling. Clinically, TNBC patients whose tumors had higher than median expression of AR had higher rates of LR after RT (HR for LR ˜3, p-value &lt;0.01, 2 independent datasets). In MVA, high AR expression was the variable most significantly associated with worse LR survival after RT in TNBC patients, outperforming all other variables (HR of 3.42; p-value &lt; 0.01).

Conclusions: Our results implicate the AR as a mediator of radioresistance in breast cancer and support the rationale for developing Sevi as a novel radiosensitizing agent in AR+ TNBC.

Citation Format: Speers CW, Chandler B, Olsen E, Wilder-Romans K, Moubadder L, Nyati S, Rae J, Hayes DF, Spratt DE, Wahl DR, Eisner J, Feng FY, Pierce LJ. Radiosensitization of androgen receptor (AR)-positive triple-negative breast cancer (TNBC) cells using seviteronel (INO-464), a selective CYP17 lyase and AR inhibitor [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-09-05.

Neoadjuvant systemic therapy in breast cancer: use and trends in radiotherapy practice

BACKGROUND

The use of neoadjuvant systemic therapy (nast) in the treatment of breast cancer is increasing, and the role of adjuvant radiation therapy (rt) in that setting is uncertain. We sought to review and report the use of nast, its trends over time, and its relationship with the prescribing patterns of locoregional rt in a provincial cancer system.

METHODS

Patients with stages i-iii breast cancer diagnosed during 2007-2012 were identified using a provincial database. Patient, tumour, and treatment characteristics were extracted. Multivariable logistic regression analyses were used to assess associations with the use of nast. Kaplan-Meier and Cox regression were used for survival analyses.

RESULTS

Of the 11,658 patients who met the inclusion criteria, 602 (5%) had received nast. Use of nast was more frequent in stage iii patients (53%) than in stages i and ii patients (2%). In clinically lymph-node positive patients, a pathology assessment was made approximately 50% of the time. Higher clinical tumour stage and increasing clinical nodal stage predicted for increasing use of nast and of nodal rt after nast, but pathologic nodal status after nast was not associated with use of nodal rt. A statistically significant survival difference was observed between patients in the nast and no-nast groups, but that significance disappeared in a multivariable Cox regression analysis.

CONCLUSIONS

This population-based study demonstrated 5% use of nast for breast cancer. Most patients received nodal rt after nast, and nodal rt was not associated with pathologic stage after nast. Findings likely reflect the realities of clinical practice and show that reliance on clinical nodal staging results in outcomes similar to those reported in the literature.

The heart of the matter: cardiac assessment in professional footballers

AIM

Sudden cardiac death is the leading medical cause of death during exercise.1 Our objective was to retrospectively analyse the routine cardiac assessment of professional footballers to aid physician management and improve player safety.

METHODS

Footballers from five professional clubs between March 2012 and October 2014 were included (n=265). All were performed in line with the recommendations of the Football Association Cardiology Committee, incorporating clinical examination, 12-lead ECG, echocardiography and health questionnaire.2 Data was retrospectively collected, inspected and analysed using Excel spreadsheets. Findings were classified as 'normal' or 'not normal', and not normal assessments were further broken down into 'clear-cut pathology' (pathology with widely accepted guidance on management) or 'grey screen'.

RESULTS

Footballers were aged 13 to 37 years, with 69% aged over 18 and 31% under. The majority of the review population was White European (66%). Of the review population 11% had 'not normal' assessments, of these assessments 83% were considered grey screens (by Consultant Cardiologist) requiring further investigation or surveillance. Overall clear-cut pathology was identified in 2%.

CONCLUSIONS

A high proportion of the players (9%) had grey screens. The majority of these were due to ECG or structural abnormalities, which are clinically challenging to differentiate from physiological adaptation of the athletic heart and potentially fatal conditions. The extent to which these findings put the athlete at risk of a life threatening cardiac event is un-?quantified. Team physician's need to be aware of managing the on-going risk with these patients and ensure suitable ?follow up and assessment on a regular basis to mitigate this.

Abstract P1-10-02: A signature predictive of early vs. late recurrence after radiation treatment (RT) for breast cancer that may inform the biology of early, aggressive recurrences

Purpose: Unmet clinical needs in breast cancer (BC) management include the identification of patients (pts) at high risk to fail locally despite standard local therapy including RT and understanding the biology of these recurrences. We previously reported1 a RT response signature and here extend those studies to identify a signature predictive of timing of recurrence after completion of RT (before or after 3 years).

Methods: Two independent patient cohorts (treated with BCS) from non-randomized clinical trials were used for training and validation. The training cohort included 119 pts with in-breast tumor recurrence and the validation cohort had 25 pts with recurrences. Initial feature selection used Spearman's rank correlation correlating gene expression (14,806 genes) to recurrence time. Genes with sig. correlation (FDR &lt;0.1) and large expression range (fold change &gt;2) were used to train an elastic net penalized Poisson regression model. This model was locked and then applied to the validation dataset. Cox regression was used for both univariate and multivariable analyses (UVA and MVA). To identify biological-related concepts, Spearman's corr. coefficients of recurrence time to gene expression within the training cohort were used to generate a pre-ranked list upon which GSEA pathway analysis was performed.

Results: Spearman's correlation identified 485 genes whose expression was significantly associated with recurrence time (early vs. late). Feature reduction further refined the gene list to 41 genes, which were retained within the signature and locked for further validation. In the training dataset the Spearman's correlation of the continuous score to recurrence time was 0.852 with a P-value of 1.3x10-34 and an AUC of 0.92. Application of this early vs late signature to an independent BC validation set accurately identifies pts with early vs. late recurrences (Spearman's corr.=0.537, p-value&lt;0.007, AUC=0.74, sensitivity=0.71, specificity=0.73, PPV=0.77, NPV=0.67). In UVA and MVA the early vs. late recurrence signature remained the most significant factor associated with recurrence time. Although independent of intrinsic subtype, GSEA analysis of the 41 genes retained within the signature identifies proliferation and EGFR concepts associated with early recurrences and luminal and ER-signaling pathways associated with late recurrences. Knockdown of genes associated with the early and late recurrences is currently underway to assess phenotypic changes (proliferation and clonogenic survival as a measure of early and durable RT response) associated with the early and late recurrence-associated genes.

Conclusion: In this study we derive a BC-specific RT signature predictive of early vs. late recurrence with biologic relevance and validate this signature for prediction of timing of recurrence in an independent clinical dataset. By identifying pts with tumors likely to recur sooner vs. later this signature has the potential to allow for a furthered understanding of the biology underlying early and late recurrences and has a potential to personalize RT, particularly in patients for whom treatment intensification is needed.

1. Clin Cancer Res. 2015 Aug 15;21(16):3667-77.

Citation Format: Speers C, Chang L, Santola A, Liu M, Zhao SG, Chandler B, Olsen E, Bartelink H, Feng FY, Pierce LJ. A signature predictive of early vs. late recurrence after radiation treatment (RT) for breast cancer that may inform the biology of early, aggressive recurrences [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-10-02.

Abstract P5-16-17: Population based long term outcomes of pathologic complete response after neoadjuvant chemotherapy in stage I-III breast cancer: The British Columbia experience

Background:

Neoadjuvant chemotherapy is a treatment option for breast cancer patients (pts) with locally advanced disease and for pts with operable breast cancer who desire breast conservation. Neoadjuvant therapy also allows for early evaluation of the effectiveness of systemic therapy. Pathologic complete response (pCR) has been shown in clinical trials to be associated with improved survival. The objective of this study was to determine if the outcomes demonstrated in clinical trials can be applied in the population based setting by comparing the outcomes of breast cancer pts who achieved pCR (no invasive disease in breast and nodes) vs. those that did not achieve a pCR.

Methods:

This is a retrospective cohort study of stage I-III invasive breast cancer pts treated with neoadjuvant chemotherapy from 2005 to 2010 in British Columbia. Cases were identified from the Breast Cancer Outcomes Unit database. Data was collected on demographics, tumor pathology, and type of treatment (chemotherapy, endocrine therapy, trastuzumab) and linked to standard clinical outcomes.

Results:

267 pts who met inclusion criteria were identified, of whom 5% had stage I, 33% Stage II and 59% Stage III breast cancer. Median follow up was 7.4 years. Overall 74 pts (28%) demonstrated a pCR and 193 pts did not. pCR pts had better 5-yr overall survival (OS) vs. non-pCR pts: 88% vs. 73% (HR 0.43, 95% CI 0.23-0.82, p=0.01). 5-yr disease free survival (DFS) was 84% in pCR pts vs. 70% in non-pCR pts (HR 0.45, 95% CI 0.24-0.83, p=0.01). Similarly, 5-yr breast cancer specific survival (BCSS) and distant disease free survival (DDFS) were significantly better in favor of the pCR cohort: HR 0.39 (95% CI 0.18-0.82, p=0.01) and HR 0.45 (95% CI 0.24-0.83, p=0.02) respectively. pCR pts were more likely to be HER2-positive and/or ER negative.

Conclusions:

Our population based results showed that early stage breast cancer pts who achieved pCR after neoadjuvant chemotherapy had better outcomes on all survival parameters compared to pts who did not achieve a pCR. This finding is consistent with results from neoadjuvant clinical trials and the FDA meta-analysis. These 'real world' results demonstrate that pCR can be used as a surrogate endpoint for survival outcomes even among non-trial pts.

Citation Format: Sun J, Gondara L, Diocee R, Speers C, Lohrisch C, Chia S. Population based long term outcomes of pathologic complete response after neoadjuvant chemotherapy in stage I-III breast cancer: The British Columbia experience [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-16-17.

Abstract P6-12-05: Targeting estrogen receptor mutations for treatment of endocrine therapy resistance in breast cancer

This abstract was withdrawn by the authors.

Abstract P5-12-10: Comparison of the efficacy of tamoxifen and aromatase inhibitors on survival in adjuvant menopausal breast cancer

Background

Meta-analyses of postmenopausal endocrine therapy and recent studies in premenopausal women suggest that aromatase inhibitors (AI) may be superior to tamoxifen (T) in preventing recurrence in early hormone receptor positive (HR+) breast cancer (BC), although there are recent concerns about the impact on overall survival (OS). The BC Cancer Agency adopted ASCO guidelines of an AI as part of adjuvant therapy for menopausal HR+ BC in 2003. Using our population based data, we sought to compare the 10 year survival outcomes for patients starting either T or AI following surgery for HR+BC.

Methods

Histopathologic and demographic data were collected for all menopausal patients referred to the BC Cancer Agency with a T1-2, node negative, HR+, HER2 negative BC diagnosed between 01/2003 and 12/2009. Patients with prior or synchronous contralateral BC were excluded. Data was cross-referenced to the provincial pharmacy database, which tracks hormone therapy. Significant factors affecting survival were identified using Cox proportional hazard model for OS and Fine and Gray's (FG) model for BC specific and Cardiac Specific Survival (CSS) with causes other than event of interest defined as competing.

Results

We identified a cohort of 3421 cases with median follow up of 7.8 years (y) for T and 7.4 y for AI. Median age was 65y in both groups, and 8.5% received chemotherapy. 47.8% of tumors were T1c and 22.2% were T2; 15.8 % were grade 3. 10 year OS was 84.4% (95% Confidence Intervals [CI] 82.4%, 86.2%) and 82.7% (95% CI 79.4%, 85.6%) for T and AI cohorts, respectively, (p= 0.02). BCSS did not differ between the groups (p=0.54). We categorized causes of death in each cohort as from BC (20.4% T, 20.6% AI), other cancers (25.4% T, 22.1% AI), cardiovascular-related (CVS) (25.8% T, 34.6% AI), thromboembolic (0.3% T, 0.7% AI %) and other (25.4%T, 19.1 % AI). Table 1 shows Univariate (U), multivariable (M), hazard ratios (Hz) and 95% CI.

Table 1 OSBCSSCSS UM (KM)UM ( FG)UM  Hz Hz HzTumour Size, continuous&lt;0.0001&lt;0.0001&lt;0.0001&lt;0.0001&lt;0.00010.0280  1.282 (1.142,1.438) 1.882 (0.631,2.090) 1.272 (1.026, 1.577)Age at dx,continuous&lt;0.0001&lt;0.00010.00190.2637&lt;0.0001&lt;0.0001  1.094 (1.080,1.108) 1.016 (0.988,1.044) 1.152 (1.122,1.183)Grade , 3 vs 1&lt;0.00010.0557&lt;0.00010.00180.29930.8719  1.341 (0.993,1.811) 2.973 (1.501,5.889) 1.051 (0.576,1.915)LVI, Yes vs No0.00040.0465&lt;0.00010.00010.24870.0671  1.357 (1.005,1.833) 2.732 (1.637,4.558) 0.474, (0.213,1.054)Chemo use, Yes or No0.0990.21220.05350.50290.02050.8710  0.748 (0.474,1.180) 1.284 (0.618,2.670) 1.128 (0.264,4.824)AI vs T0.020.29270.59250.25540.00410.0123  1.124 (1.142,1.438) 0.742 (0.443,1.241) 1.658 (1.116,2.463)

Conclusion

While trials show that AIs improve relapse free survival after menopausal HR+BC, their impact on BCSS has been minimal. By contrast they may contribute to CVS deaths, as suggested by our data. We plan to explore this observation further by examining baseline cardiac risk factors within our T and AI cohorts, and by exploring OS, BCSS, and CSS among patients switching to AI after starting T, to identify the optimal adjuvant hormone therapy strategy for menopausal women with HR+ early BC.

Citation Format: Chay WY, Speers C, Gondara L, Tyldesley S, Ellard SL, Lohrisch CA, Gelmon KA. Comparison of the efficacy of tamoxifen and aromatase inhibitors on survival in adjuvant menopausal breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-12-10.

Abstract S4-05: Interrogating the landscape of long noncoding RNAs in breast cancer to identify predictors of tamoxifen resistance

Background: We previously performed an informatics-based analysis on RNA sequencing libraries from 7,256 tumor and normal tissue specimens to delineate the landscape of long noncoding RNAs (lncRNAs) in the human transcriptome. This analysis identified 58,648 lncRNAs, including over 45,000 novel transcripts (Iyer MK et al, Nature Genetics, 2015). We now interrogate this lncRNA compendium to identify top candidate estrogen receptor (ER)-associated lncRNAs in breast cancer and characterize their association with disease progression.

Methods: To prioritize differentially expressed lncRNAs in cancer vs normal tissue, and in ER+ vs ER- disease, we performed Sample Set Enrichment Analysis (SSEA) on &gt;1000 RNA Seq libraries, from breast cancer and normal tissue samples from The Cancer Genome Atlas project. The effect of the top prioritized lncRNA on cancer phenotypes was studied via in vitro proliferation, colony formation, invasion and tamoxifen resistance assays in MCF7 and T47D cells, and via in vivo mouse xenograft studies and chick chorioallantoic membrane (CAM) assays. To study the mechanism by which this lncRNA promotes tumor progression, we identified its top protein interactors and subdomains responsible for function, and then studied the effects of disrupting function of this lncRNA on cancer phenotypes. Finally, in a "guilt-by-association" study, we developed a signature of 150 protein coding genes most strongly associated with our lncRNA of interest, and investigated the association of this signature with clinical outcomes using Oncomine analyses.

Results: SSEA analysis on over 1000 TCGA samples nominated Breast Cancer Associated Transcript (BRCAT 431) as the top overexpressed ER-regulated lncRNA in breast cancer. In vitro experiments demonstrate that siRNA-mediated knockdown of BRCAT431 resulted in significantly decreased proliferation, colony formation, and invasion (by &gt;50% in most assays). Tamoxifen resistance was associated with significantly increased BRCAT431 levels in both MCF7 and T47D cells, and knockdown of BRCAT431 reversed tamoxifen resistance. In vivo xenograft and CAM studies demonstrate that knockdown of BRCAT431 also significantly decreased xenograft growth and tumor invasion by &gt;50%. RNA pulldown followed by mass spectrometry identified the RNA binding protein hnRNPL as a key protein interacting with BRCAT431. Deletion studies identified a 27 base region of BRCAT431 necessary for its interaction with hnRNPL, and loss of this region abrogated BRCAT431- induced invasion. Finally, guilt-by-association studies demonstrate a strong association between BRCAT431 overexpression and tumor grade, recurrence, and metastases.

Conclusion: In this study, we develop the largest reported compendia of breast cancer lncRNAs. We prioritize BRCAT431 as the top lncRNA upregulated in ER-positive breast cancers, and demonstrate that it confers aggressive oncogenic phenotypes in vitro and in vivo. We identify a novel mechanism by which this lncRNA functions. Our results suggest that by promoting tamoxifen resistance, BRCAT431 increases the clinical risk of recurrence and metastases in breast cancer. Overall, this study supports the rationale for investigating lncRNAs as novel biomarkers and therapeutic targets in breast cancer.

Citation Format: Feng FY, Niknafs Y, Han S, Ma T, Speers C, Malik R, Evans J, Zhang C, Pierce LJ, Hayes DF, Rae JM, Chinnaiyan AM. Interrogating the landscape of long noncoding RNAs in breast cancer to identify predictors of tamoxifen resistance. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S4-05.

Population-based analysis of the impact and generalizability of the NSABP-B24 study on endocrine therapy for patients with ductal carcinoma in situ of the breast

BACKGROUND

In 1999, the National Surgical Adjuvant Breast and Bowel Project (NSABP)-B24 trial demonstrated that tamoxifen reduced relapse risk in women with ductal carcinoma in situ (DCIS) treated with breast-conserving surgery (BCS) and radiotherapy (RT). In 2002, Allred's subgroup analysis showed that tamoxifen mainly benefitted estrogen receptor (ER)-positive disease. This study evaluates the impact and generalizability of these trial findings at the population level.

PATIENTS AND METHODS

From 1989 to 2009, 2061 women with DCIS underwent BCS + RT in British Columbia. The following cohorts were analyzed: (1) pre-NSABP-B24 era (1989-1998, N = 417); (2) post-NSABP-B24 era (2000-2009, N = 1548). Cohort 2 was further divided into pre- and post-Allred eras.

RESULTS

Endocrine therapy (ET) was used in 404/2061 (20%) patients. Median age of patients treated with compared with without ET, was 53 versus 57 years, (P < 0.0005). One of 417 (0.2%) versus 399/1548 (26%) patients took ET before versus after NSABP-B24. Among the post-Allred era cohort treated with ET (N = 227), tumors were ER-positive in 65%, ER-negative in 1%, and ER-unknown in 33%; whereas of those treated without ET (N = 801), ER was positive in 43%, negative in 15%, and unknown in 42% (P < 0.0005). On multivariable analysis of the post-NSABP-B24 era, ET was associated with improved event-free survival (EFS) (hazard ratio 0.6; P = 0.02); 5-year EFS were 96.9% with ET versus 94.5% without ET.

CONCLUSIONS

ET use in DCIS patients treated with BCS + RT increased significantly after the NSABP-B24 study. ER+ disease and younger age were associated with increased ET use. ET was associated with improved EFS, confirming the generalizability of trial data at a population level.