Concurrent use of palbociclib and radiation therapy: single-centre experience and review of the literature

Radiosensitizing effects of CDK4/6 inhibitors in hormone receptor-positive and HER2-negative breast cancer mediated downregulation of DNA repair mechanism and NF-κB-signaling pathway

CDK4/6 inhibitors combined with endocrine therapy prolonged survival in hormone receptor (HR)-positive and HER2-negative advanced breast cancer. We investigated whether CDK4/6 inhibitors enhance radiosensitivity and their underlying mechanisms of this subtype of breast cancer. In vitro and in vivo experiments were conducted using two HR-positive and HER2-negative breast cancer cell lines (MCF-7 and T-47D), CDK4/6 inhibitors (ribociclib and palbociclib) and radiotherapy (RT) to assess the biological functions and mechanisms. The radiation-enhancing effect was assessed using clonogenic assays; γH2AX and 53BP1 levels were assessed by immunofluorescence to evaluate DNA damage. The levels of phospho (p)-ERK, c-Myc, and DNA-double strand break (DSB)-related molecules, p-DNA-PKcs, Rad51, and p-ATM, were assessed by western blotting. We used an NF-κB p65 transcription factor assay kit to evaluate NF-κB activity. We evaluated the antitumor effect of the combination of RT and ribociclib through the MCF-7 orthotopic xenograft model. The synergistic effects of combining RT with ribociclib and palbociclib pretreatment were demonstrated by clonogenic assay. CDK4/6 inhibitors synergistically increased the numbers of RT-induced γH2AX and 53BP1, downregulated the expression of p-DNA-PKcs, Rad51 and p-ATM activated by RT, and reduced RT-triggering p-ERK expression, NF-κB activation, and its down-streaming gene, c-Myc. Combined ribociclib and RT reduced the growth of MCF-7 cell xenograft tumors, and downregulated the immunohistochemical expression of p-ERK, p-NF-κB p65, and c-Myc compared to that in the control group. Combining CDK4/6 inhibitors enhanced radiosensitivity of HR-positive and HER2-negative breast cancer cells at least by reducing DNA-DSB repair and weakening the activation of ERK and NF-κB signaling by RT.

Locoregional Radiotherapy in Patients with Advanced Breast Cancer Treated with Cyclin-Dependent Kinase 4/6 Inhibitors Based on Real-World Data

BACKGROUND

The use of locoregional radiotherapy (RT) in patients with advanced ER-positive, HER2-negative breast cancer remains a topic of ongoing debate. In this study, we aimed to evaluate the efficacy of locoregional RT in advanced breast cancer patients treated with cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in a first-line setting.

METHODS

We conducted a retrospective analysis of patients diagnosed with advanced breast cancer between 2018 and 2023 who received treatment with CDK4/6i and underwent locoregional radiotherapy.

RESULTS

Among the 371 patients treated with CDK4/6i as part of their first-line therapy, 23 received locoregional RT either concurrently or sequentially with CDK4/6 inhibitors. Disease progression within the breast occurred in 19 patients (5.1%). Among these cases, five patients had previously undergone breast RT (5/23, 21.7%), while 14 did not (14/348, 4.0%, p = 0.004). All cases of local progression after RT followed palliative doses and were accompanied by early systemic progression. The 2-year PFS in the entire cohort of patients treated with locoregional RT was 65.7% (95% CI: 40.5-82.3%). Notably, patients who received higher RT doses had longer 2-year PFS (83.3%, 95% CI: 27.3-97.5%) than those with palliative RT doses (59.3%, 95% CI: 30.7-79.3%); however, the results were not statistically significant (p = 0.58). Furthermore, the 2-year local control in the entire cohort with locoregional RT was 73.0% (95% CI: 46.5-87.9%). Importantly, no local progression was observed after RT when using high doses.

CONCLUSIONS

The addition of locoregional radiotherapy to first-line CDK4/6 inhibitors warrants further investigation across various clinical scenarios in advanced breast cancer. Palliative radiation regimens delivered early in breast oligoprogression may not always suffice, emphasizing the need for comprehensive studies in this context.

Concurrent use of Radiotherapy and Ribociclib: Preliminary Results and Review of the Literature

OBJECTIVES

In the recent MONALEESA-2, MONALEESA-3, and MONALEESA-7 clinical trials, the addition of ribociclib, a CDK4/6 inhibitor, to standard endocrine therapy significantly improved progression-free survival (PFS) compared with hormone therapy alone in the treatment of locally advanced or metastatic estrogen receptor-positive (ER) and HER2-negative breast cancer. However, its toxicity raises concerns when administered concomitantly with radiotherapy, leading most radiotherapists and medical oncologists to prefer to discontinue Ribociclib during radiotherapy (RT). Although there are insufficient published data on this combination, our preliminary experience with the first 2 patients treated at Institut Curie suggests promising results when using Ribociclib with Letrozole or Fulvestrant concurrently with palliative radiotherapy in the treatment of metastatic breast cancer. Our study aimed to evaluate the safety of combining Ribociclib with palliative radiotherapy in patients with metastatic breast cancer, providing crucial insights for clinical decision-making.

METHODS

A retrospective analysis was conducted on patients treated for hormone receptor-positive metastatic breast cancer with Ribociclib and concurrent radiotherapy at the Institut Curie (Paris, France) between September 2023 and April 2024. Among 38 patients who received Ribociclib and underwent irradiation, 36 temporarily suspended Ribociclib during radiotherapy, while 2 continued Ribociclib concurrently and were included in the analysis. Palliative radiotherapy was administered using volumetric modulated arc therapy, delivering 20 Gy in 5 fractions to bone metastatic sites. Ribociclib was given at 600 mg/day with hormonotherapy. Follow-up was conducted from the last day of RT until the last medical consultation. Toxicities were graded using CTCAE V5.0.

RESULTS

Two patients received Ribociclib concomitantly with radiotherapy, experiencing pain relief without interruptions in RT. However, Ribociclib treatment was halted in both cases due to grade 3 neutropenia and grade 1 QTc interval prolongation, respectively. One patient had a dose reduction to 400 mg due to neutropenia, with favorable outcomes observed. Both patients continued Ribociclib treatment, with one achieving complete remission and the other partial remission of bone disease. No late toxicities were observed.

CONCLUSION

Despite the need for further investigation, our results suggest safety consistent with pivotal trials, advocating for a prospective cooperative data collection initiative to explore this combined strategy further, potentially revolutionizing metastatic breast cancer management.

Radiation-induced gastric injury during radiotherapy: molecular mechanisms and clinical treatment

Radiotherapy (RT) has been the standard of care for treating a multitude of cancer types. Radiation-induced gastric injury (RIGI) is a common complication of RT for thoracic and abdominal tumors. It manifests acutely as radiation gastritis or gastric ulcers, and chronically as chronic atrophic gastritis or intestinal metaplasia. In recent years, studies have shown that intracellular signals such as oxidative stress response, p38/MAPK pathway and transforming growth factor-β signaling pathway are involved in the progression of RIGI. This review also summarized the risk factors, diagnosis and treatment of this disease. However, the root of therapeutic challenges lies in the incomplete understanding of the mechanisms. Here, we also highlight the potential mechanistic, diagnostic and therapeutic directions of RIGI.

Safety and feasibility of CDK4/6 inhibitors treatment combined with radiotherapy in patients with HR-positive/HER2-negative breast cancer. A systematic review and meta-analysis

BACKGROUND AND PURPOSE

The addition of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) to endocrine therapy in hormone receptor-positive (HR+) human epidermal growth factor 2-negative (HER2-) breast cancer has led to practice-changing improvements in overall survival. However, there are conflicting data concerning the safety of CDK4/6i combination with radiotherapy, and no consensus guidelines exist to guide practice. We conducted a meta-analysis to assess the safety and feasibility of CDK4/6i treatment with radiotherapy.

MATERIALS AND METHODS

A comprehensive search was performed in PubMed/MEDLINE, Web of Science, and Scopus, for studies in advanced/metastatic breast cancer receiving CDK4/6i and radiotherapy with the provided safety data on the occurrence of toxicity. The main outcomes were safety (grade 3-5 adverse events), CDK 4/6i dose reduction, and the discontinuation rate due to toxicity.

RESULTS

Fifteen studies comprising 1133 patients with HR+/HER2- breast cancer patients were included. Among them, 617 pts received CDK4/6i and radiotherapy; the median follow-up was 17.0 months (IQR 9.2 - 18.0), and the median age was 58.8 years (IQR 55.5---62.5). The pooled prevalence of severe hematologic toxicity was 29.4% (95% CI 14.0% - 47.4%; I2 = 93%; τ2 = 0.084; p < 0.01 and severe non-hematologic toxicity was 2.8% (95% CI 1.1% - 4.8%; I2 = 0%; τ2 = 0.0; p = 0.67). The pooled prevalence of CDK4/6i dose reduction was 24.0% (95% CI 11.1% - 39.4%; I2 = 90%; τ2 = 0.052; p < 0.01) with no difference between CDK4/6i plus RT vs. CDK4/6i (odds ratio of 0.934; 95% CI 0.66 - 1.33; I2 = 0%; τ2 = 0.0; p = 0.56). The pooled prevalence of CDK4/6i discontinuation due to toxicity was 2.3% (95% CI 0.4% - 5.2%; I2 = 23%; τ2 = 0.002; p = 0.24).

CONCLUSION

The findings of this study suggest that radiotherapy in addition to CDK4/6i treatment in breast cancer patients is generally safe and well tolerated and remains a viable treatment option.

Integration of Postoperative Radiation Therapy with Cyclin-Dependent Kinase (CDK) Inhibitors

PURPOSE OF REVIEW

Sequential use of radiation therapy before cyclin-dependent kinase (CDK) inhibitors in women with early breast cancer seems reasonable and with a low toxicity rate. This study aimed to evaluate the possible interaction between RT and CDK inhibitors in the adjuvant setting for patients with positive hormone receptors and HER-2 negative, investigating toxicity and the treatment sequencing.

RECENT FINDINGS

CDK inhibitors have been studied in patients with localized breast cancer and can improve invasive disease-free survival outcomes. Regarding the time of RT, all trials used CDK inhibitors after the RT. Interruptions in the CDK inhibitors were performed in 27.1% in Pallas, 17.5% in Penelope-B, and 16.6% in Monarch-E trials due to adverse events. Data from the Natalee trial are still not reported. The main adverse event grade III was neutropenia, with good resolution of the symptoms over time. CDK inhibitors applied sequentially and after RT postoperative showed a low profile of acute toxicity and suitable oncological outcomes.

Safety profile of cyclin-dependent kinase (CDK) 4/6 inhibitors with concurrent radiation therapy: A systematic review and meta-analysis

The cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have become the standard of care for hormone receptor-positive (HR + ) and human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer, improving survival outcomes compared to endocrine therapy alone. Abemaciclib and ribociclib, in combination with endocrine therapy, have demonstrated significant benefits in invasive disease-free survival for high-risk HR+/HER2- early breast cancer patients. Each CDK4/6i-palbociclib, ribociclib, and abemaciclib-exhibits distinct toxicity profiles. Radiation therapy (RT) can be delivered with a palliative or ablative intent, particularly using stereotactic body radiation therapy for oligometastatic or oligoprogressive disease. However, pivotal randomized trials lack information on concomitant CDK4/6i and RT, and existing preclinical and clinical data on the potential combined toxicities are limited and conflicting. As part of a broader effort to establish international consensus recommendations for integrating RT and targeted agents in breast cancer treatment, we conducted a systematic review and meta-analysis to evaluate the safety profile of combining CDK4/6i with palliative and ablative RT in both metastatic and early breast cancer settings.

[Radiotherapy and targeted therapy for the management of breast cancer: A review]

The purpose of this study was to review the current knowledge regarding combinations of the most commonly used targeted therapies or those under development for the management of breast cancer with radiation therapy. Several studies have shown that the combination of radiation therapy and tamoxifen increased the risk of radiation-induced lung toxicity; therefore, the two modalities are generally not given concurrently. The combination of HER2 inhibitors (trastuzumab, pertuzumab) and radiation therapy appeared to be safe. However, trastuzumab emtansine (T-DM1) should not be given concomitantly with brain radiation therapy because this combination may increase the risk of brain radionecrosis. The combination of radiation therapy with other new targeted therapies such as new selective estrogen receptor modulators (SERDs), lapatinib, cell cycle inhibitors, immune checkpoint inhibitors, or molecules acting on DNA damage repair seems feasible but has been mainly evaluated on retrospective or prospective studies with small numbers of patients. Moreover, there is a great heterogeneity between these studies regarding the dose and fractionation used in radiotherapy, the dosage of systemic treatments and the sequence of treatments used. Therefore, the combination of these new molecules with radiotherapy should be proposed sparingly, under close monitoring, pending the ongoing prospective studies cited in this review.

[Targeted systemic treatments and locoregional radiotherapy for breast cancer: Can we expect a benefit from the potentiation of local treatment?]

Breast cancer is the first most common cancer worldwide, and radiation therapy has a major role to play in locoregional adjuvant treatment. In recent years, we have seen the emergence of adjuvant targeted systemic therapies improving the prognosis of patients at high risk of recurrence. Practices concerning combinations of targeted therapies and locoregional radiation therapy for non-metastatic breast cancers often remain heterogeneous due to the low level of evidence and lack of validated recommendations. This literature review covers immunotherapy, CDK 4/6 inhibitors, PARP inhibitors and anti-Her2 therapies. Combining these targeted systemic therapies with radiation therapy could potentiate local treatment. The optimal therapeutic sequence and fractionation for maximum synergistic effect remain to be defined. However, while efficacy may be enhanced, radiosensitization of healthy tissue may also lead to increased toxicity. It appears possible to continue immunotherapy, trastuzumab, pertuzumab, TDM-1 or lapatinib during locoregional breast and lymph node irradiation. PARP inhibitors and CDK4/6 inhibitors are still to be suspended, due to the lack of data in the adjuvant setting and their short half-life, which does not necessitate prolonged discontinuation. As with the new antibody-drug conjugates, prospective data are needed in conjunction with adjuvant radiation therapy.

Interstitial lung disease and CDK4/6 inhibitors in the treatment of breast cancer

INTRODUCTION

CDK4/6 inhibitors have changed the treatment paradigm of many patients living with metastatic and early-stage high-risk hormone receptor (HR)-positive breast cancer. Even though patients and clinicians are aware and learning how to manage common adverse events, such as bone marrow suppression and gastrointestinal toxicities, there are less common and potentially severe adverse events, such as interstitial lung disease (ILD), that require special consideration.

AREAS COVERED

In this narrative review, we discuss the incidence, mechanism, and treatment of CDK4/6 inhibitor associated ILD.

EXPERT OPINION

CDK4/6 inhibitors in combination with endocrine therapy (ET) are standard treatment for HR-positive, HER2-negative metastatic breast cancer and for selected patients with early stage HR-positive breast cancer. Common toxicities of these medications are often controlled with dose reductions, dose interruptions, and/or prophylactic medications, such as antidiarrheals. However, there are a small subset of patients at risk for less common and potentially severe toxicities, such as ILD. Individualized risk should be considered, including underlying lung disease, thrombosis risk and drug-drug interactions, in order to counsel patients about the risk of ILD.

Safety of CDK4/6 Inhibitors Combined with Radiotherapy in Patients with Metastatic Breast Cancer: A Review of the Literature

Recent evidence suggests that cyclin-dependent kinase 4/6 (CDK4/6) inhibitors significantly improve progression-free survival and overall survival among metastatic breast cancer patients. However, given the effects on cell cycle arrest, there is potential for CDK4/6 inhibitors and radiotherapy (RT) to work synergistically, enhancing the effect and toxicities of RT. A comprehensive review of the literature on the combination of RT and CDK4/6 inhibitors was performed with 19 eligible studies included in the final analysis. A total of 373 patients who received radiotherapy combined with CDK4/6 inhibitors were evaluated across 9 retrospective studies, 4 case reports, 3 case series, and 3 letters to the editor. The CDK4/6 inhibitor used, RT target, and RT technique were assessed in terms of toxicities. This literature review demonstrates generally limited toxicities with the combination of CDK4/6 inhibitors and palliative radiotherapy to metastatic breast cancer patients. The current evidence is nonetheless limited, and further results of ongoing prospective clinical trials will help clarify whether these treatments can be safely combined.

[Biological, preclinical and clinical aspects of the association between radiation therapy and CDK4/6 inhibitors]

Several clinical studies have shown that CDK4/6 inhibitors (CDK4/6i) improve survival in patients with metastatic or locally advanced HR-positive, HER-2-negative breast cancer (BC). The aim of this review was to synthesize the biological, preclinical and clinical aspects of the treatment of BC with CDK4/6i, with a focus on the combination of CDK4/6i and radiotherapy. The DNA damage induced after exposure of cells to ionizing radiation activates control pathways that inhibit cell progression in the G1 and G2 phases and induce a transient delay in progression in the S phase. These checkpoints are in particular mediated by cyclin-dependent kinases (CDK) 4/6 activated by cyclin D1. Several preclinical studies have shown that CDK4/6i could be used as radiosensitizers in non-small cell lung cancer, medulloblastoma, brainstem glioma and breast cancer. CDK4/6 inhibition also protected against radiation-induced intestinal toxicities by inducing redistribution of quiescent intestinal progenitor cells, making them less radiosensitive. Clinical data on the combination of CDK inhibitors and radiotherapy for both locoregional and metastatic irradiation are based on retrospective data. Nevertheless, the most optimal therapeutic sequence would be radiotherapy followed by palbociclib. Pending prospective clinical trials, the concomitant combination of the two treatments should be done under close supervision.

Incidence of and risk factors for non-hematologic toxicity with combined radiotherapy and CDK4/6 inhibitors in metastatic breast cancer using dose-volume parameters analysis: a multicenter cohort study

BACKGROUND

There is a lack of data on combined radiotherapy (RT) and cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) risk factors and toxicity. This study aimed to assess the incidence of and risk factors for non-hematologic toxicities in patients treated with combined RT and CDK4/6i using dose-volume parameter analysis.

METHODS

We conducted a retrospective multicenter cohort study of patients with metastatic breast cancer receiving RT within 14 days of CDK4/6i use. The endpoint was non-hematologic toxicities. Patient characteristics and RT treatment planning data were compared between the moderate or higher toxicities (≥ grade 2) group and the non-moderate toxicities group.

RESULTS

Sixty patients were included in the study. CDK4/6i was provided at a median daily dose of 125 mg and 200 mg for palbociclib and abemaciclib, respectively. In patients who received concurrent RT and CDK4/6i (N = 29), the median concurrent prescribed duration of CDK4/6i was 14 days. The median delivered RT dose was 30 Gy and 10 fractions. The rate of grade 2 and 3 non-hematologic toxicities was 30% and 2%, respectively. There was no difference in toxicity between concurrent and sequential use of CDK4/6i. The moderate pneumonitis group had a larger lung V20 equivalent dose of 2 Gy per fraction and planning target volume than the non-moderate pneumonitis group.

CONCLUSIONS

Moderate toxicities are frequent with combined RT and CDK4/6i. Caution is necessary concerning the combined RT and CDK4/6i. Particularly, reducing the dose to normal organs is necessary for combined RT and CDK4/6i.

Safety and Feasibility of Radiation Therapy Combined with CDK 4/6 Inhibitors in the Management of Advanced Breast Cancer

The addition of CDK4/6 inhibitors to endocrine therapy in advanced hormone receptor-positive HER2-negative breast cancer has led to practice-changing improvements in overall survival. However, data concerning the safety of CDK4/6i combination with radiotherapy (RT) are conflicting. A retrospective evaluation of 288 advanced breast cancer patients (pts) treated with CDK4/6i was performed, and 100 pts also received RT. Forty-six pts received 63 RT courses concurrently and fifty-four sequentially before CDK4/6i initiation (76 RT courses). Neutropenia was common (79%) and more frequent during and after concurrent RT than sequential RT (86% vs. 76%); however, CDK4/6i dose reduction rates were similar. In patients treated with CDK4/6i alone, the dose reduction rate was 42% (79 pts) versus 38% with combined therapy, and 5% discontinued treatment due to toxicity in the combined group. The risk of CDK4/6i dose reduction was correlated with neutropenia grade, RT performed within the first two CDK4/6i cycles, and more than one concurrent RT; a tendency was observed in concurrent bone irradiation. However, on multivariate regression analysis, only ECOG 1 performance status and severe neutropenia at the beginning of the second cycle were found to be associated with a higher risk of CDK4/6i dose reduction. This largest single-center experience published to date confirmed the acceptable safety profile of the CDK4/6i and RT combination without a significantly increased toxicity compared with CDK4/6i alone. However, one might delay RT for the first two CDK4/6i cycles, when myelotoxic AE are most common.

Safety of CDK4/6 inhibitors and concomitant radiation therapy in patients affected by metastatic breast cancer

PURPOSE

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) currently represent the standard of care for the initial treatment of patients with metastatic hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer. The aim of our study is to evaluate the safety of the use of concomitant radiation therapy (RT) in a consecutive series of HR+/HER2- patients treated in two academic institutions with CDK4/6i in the metastatic setting.

METHODS AND MATERIALS

From September 2017 to February 2020, we retrospectively collected and analysed data on a sequential series of patients treated with CDK4/6i, receiving RT or not, at two European institutions. Primary outcome of the study was the association between RT and any adverse events (AEs) ≥ G3. Secondary outcomes were the association between RT and any AEs (any grade), CDK4/6i dose reduction rate, and CDK4/6i treatment discontinuation rate.

RESULTS

We analysed a total of 132 consecutive women; RT was prescribed in 57 (43.2%) patients (70 irradiated lesions). The median age of the series was 52.1 years (range 32.3-78.2). Concomitant RT administration was not significantly related to higher AEs ≥ G3 (p = 0.19) and any grade AEs (p = 1.0); there was no association with RT and CDK4/6i dose reduction (p = 0.49) and discontinuation rates (p = 0.14). At a median follow-up of 18.8 months, the progression-free survival (PFS) rate was 35% and the overall survival (OS) rate was 38.7% in the whole group. The use of concomitant RT did not affect both PFS (p = 0.71) and OS rates (p = 0.55).

CONCLUSIONS

Our data are encouraging regarding the safety of this combination, showing that concurrent RT did not increase severe toxicity and did not have an impact on systemic treatment conduction.

Radiotherapy of the Primary Disease for Synchronous Metastatic Cancer: A Systematic Review

In the case of synchronous metastatic disease, the local treatment of primary tumors by radiotherapy has long been reserved for palliative indications. The emergence of the concept of oligometastatic and oligopersistent diseases, the advent of new systemic therapies enabling longer overall survival with an enhanced quality of life, a better understanding of the biologic history of metastatic spread, and technical advances in radiation therapy are revolutionizing the management of patients with de novo metastatic cancer. The prognosis of these patients has been markedly improved and many studies have investigated the survival benefits from the local treatment of various primary tumors in cases of advanced disease at the time of diagnosis or in the case of oligopersistence. This article provides an update on the place of irradiation of the primary tumor in cancer with synchronous metastases, and discusses its interest through published or ongoing trials.

Radiotherapy and CDK inhibitors: Opportunities and risks

CDK4/6 inhibitors are nowadays commonly used in metastatic HR+/HER2- breast cancer. Herein, we report a literature review regarding the benefits and risks of their combination with radiotherapy. Numerous pre-clinical studies have indeed shown a potential synergistic effect of these treatments in combination with radiotherapy in various types of cancers. On the other hand, some retrospective clinical studies have reported increased acute toxicity in case of digestive or pulmonary irradiation; therefore, it is advisable to discontinue CDK4/6 inhibitors before starting irradiation. Several prospective clinical trials are currently ongoing to assess the feasibility of this combination.

Regression of choroidal metastasis from breast carcinoma with palbociclib

Background

Uveal metastasis is reported to be the most common intraocular malignancy. The most common site of origin of ocular metastases in females is the breast. In some cases, uveal metastatic lesions respond to systemic chemotherapy. We report a case of a patient who developed choroidal metastasis, while on endocrine therapy with selective estrogen receptor modulator (SERM), tamoxifen, for estrogen receptor (ER) positive, progesterone receptor (PR) positive and (human epidermal growth factor receptor 2) HER2 negative primary breast carcinoma, which then regressed following systemic chemotherapy with palbociclib.

Case description

An 83-year-old female, with a history of modified radical mastectomy, chemotherapy and radiation therapy for infiltrating duct carcinoma of the breast, presented with a choroidal metastatic lesion in the left eye along with liver and lung metastases, 3 years after the primary carcinoma was treated. At the time of presentation, she was on tamoxifen. The choroidal tumor showed regression after the introduction of palbociclib, a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor.

Conclusion

This report highlights the use of palbociclib, in the palliative treatment of choroidal metastasis from primary breast cancer. The use of chemotherapy for choroidal metastasis can help avoid external beam radiation therapy and its concurrent side effects. Although there are a few reports involving the use of palbociclib for metastatic breast carcinoma, all of those have been in conjunction with and/or following non-response to other treatment modalities. Ours is the first report wherein palbociclib has been used as the first-line palliative chemotherapy and helped in regression of choroidal metastasis.

Radiotherapy with Cyclin-Dependent Kinase 4/6 Inhibitors: A Multi-institutional Safety and Toxicity Study

PURPOSE

To investigate radiotherapy (RT) toxicity when given with Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6i) compared to RT alone.

METHODS AND MATERIALS

We conducted a retrospective cohort study of patients with hormonal receptor-positive and human epidermal growth factor-2 negative metastatic breast cancer treated with RT at four cancer centers in Alberta, Canada between 2016 and 2020. Toxicity in patients treated with RT within 30 days of initiating to discontinuing CDK4/6i (RT+CDK4/6i) was compared to toxicity of RT in CDK4/6i naïve patients (RT alone). The primary outcome was acute grade (G) II or higher, non-hematological toxicity within 30 days of RT. We also explored toxicity based on the timing of RT (prior, concurrent, post) in relation to CDK4/6i. Propensity score matching was applied to create comparable cohorts. A generalized linear mixed model was used to evaluate factors associated with acute toxicity.

RESULTS

132 patients (220 RT sites) in the RT+CDK4/6i and 53 patients (93 RT sites) in RT alone were eligible. The rate of acute GII or higher non-hematological toxicity was 11.5% vs. 7%, respectively (p=0.439), and acute GIII or higher non-hematological toxicity was 3.7% vs. 0%, respectively (p=0.151). Acute toxicity in RT+CDK4/6i group was mainly observed when RT was given concurrently (67%) with most of the GIII toxicity recorded. After propensity score matching, the association of acute toxicity with RT+CDK4/6i vs. RT alone was not significant on multivariable analysis, Odds Ratio 3.13 (95% confidence interval: 0.74 - 13.2; p=0.121).

CONCLUSIONS

We did not observe a significant association between CDK4/6i use and acute, GII or higher, non-hematological toxicity, in women with metastatic breast cancer receiving palliative RT. Given the findings of GIII toxicity, caution is advised whenever CDK4/6i is given concurrently with RT.

Safety and Tolerability of Metastasis Directed Radiotherapy in the Era of Evolving Systemic, Immune and Targeted Therapies

AbstractPurpose

Systemic, immune, and target therapies are growing in use in the management of metastatic cancers. The aim of this review was to describe up-to-date published data on the safety and tolerability of metastasis-directed hypofractionated radiation therapy (RT) when combined with newer systemic, immune, and targeted therapies and to provide suggested strategies to mitigate potential toxicities in the clinical setting.

Methods and Materials

A comprehensive search was performed for the time period between 1946 and August 2021 using predetermined keywords describing the use of noncentral nervous system palliative RT with commonly used targeted systemic therapies on PubMed and Medline databases. A total of 1022 articles were screened, and 130 met prespecified criteria to be included in this review.

Results

BRAF and MEK inhibitors are reported to be toxic when given concurrently with RT; suspension 3 days and 1 to 2 days, respectively, prior and post-RT is suggested. Cetuximab, erlotinib/gefitinib, and osimertinib were generally safe to use concomitantly with conventional radiation. But in a palliative/hypofractionated RT setting, suspending cetuximab during radiation week, erlotinib/gefitinib 1 to 2 days, and osimertinib ≥2 days pre- and post-RT is suggested. Vascular endothelial growth factor inhibitors such as bevacizumab reported substantial toxicities, and the suggestion is to suspend 4 weeks before and after radiation. Less data exist on sorafenib and sunitinib; 5 to 10 days suspension before and after RT should be considered. As a precaution, until further data are available, for cyclin-dependent kinase 4-6 inhibitors, consideration of suspending treatment 1 to 2 days before and after RT should be given. Ipilimumab should be suspended 2 days before and after RT, and insufficient data exist for other immunotherapy agents. Trastuzumab and pertuzumab are generally safe to use in combination with RT, but insufficient data exist for other HER2 target therapy.

Conclusions

Suggested approaches are described, using up-to-date literature, to aid clinicians in navigating the integration of newer targeted agents with hypofractionated palliative and/or ablative metastatic RT. Further prospective studies are required.

Multidisciplinary Treatment of Non-Spine Bone Metastases: Results of a Modified Delphi Consensus Process

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Evidence is emerging for new paradigms in the management of non-spine bone metastases.

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Consensus was feasible amongst physicians in both academic and community-based practice settings.

•

Topics deemed of highest importance for consensus included referral for surgical stabilization and approach to peri-operative radiation, preferred radiation fractionation and appropriate use of stereotactic techniques, and clinical scenarios classified as potentially “complex” warranting multidisciplinary discussion.

Purpose

Methods and Materials

Results

Conclusions

Radiotherapy as a tool to elicit clinically actionable signalling pathways in cancer

A variety of targeted anticancer agents have been successfully introduced into clinical practice, largely reflecting their ability to inhibit specific molecular alterations that are required for disease progression. However, not all malignant cells rely on such alterations to survive, proliferate, disseminate and/or evade anticancer immunity, implying that many tumours are intrinsically resistant to targeted therapies. Radiotherapy is well known for its ability to activate cytotoxic signalling pathways that ultimately promote the death of cancer cells, as well as numerous cytoprotective mechanisms that are elicited by cellular damage. Importantly, many cytoprotective mechanisms elicited by radiotherapy can be abrogated by targeted anticancer agents, suggesting that radiotherapy could be harnessed to enhance the clinical efficacy of these drugs. In this Review, we discuss preclinical and clinical data that introduce radiotherapy as a tool to elicit or amplify clinically actionable signalling pathways in patients with cancer.

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.

Combination of Modern Radiotherapy and New Targeted Treatments for Breast Cancer Management

Simple Summary

Since the introduction of hormone therapy for the treatment of breast cancer (BC) three decades ago, many new targeted therapies have been developed. Some of them are currently used, such as HER2 inhibitors, while others are still under development, such as cell cycle (CDK) inhibitors, immune checkpoint (PD1/PDL1) inhibitors, or molecules acting on DNA damage (PARP) repair. Besides this, radiation therapy (RT) is commonly used either as adjuvant treatment for early BC after breast conservative surgery or in palliative intent for the treatment of metastatic sites. Our research has shown that the combinations of the most commonly used targeted treatments and RT were feasible with a few toxicities. Nevertheless, most of the knowledge on this subject is based on retrospective studies and a small number of patients and care should be taken in this setting until these results would be confirmed in prospective randomized studies.

Abstract

Background: The objective of the present study was to review the essential knowledge about the combinations of the most commonly used or under development targeted treatments and radiation therapy (RT). Methods: Preclinical and clinical studies investigating this combination were extensively reviewed. Results: Several studies showed that the combination of RT and tamoxifen increased the risk of radiation-induced pulmonary toxicity; therefore, both modalities should not be given concomitantly. The combination of HER2 inhibitors (trastuzumab, pertuzumab) and RT seems to be safe. However, trastuzumab emtansine (T-DM1) should not be administered concurrently with brain RT since this combination could increase the risk of brain radionecrosis. The combination of RT and other new target treatments such as selective estrogen receptor degradants, lapatinib, cell cycle inhibitors, immune checkpoint inhibitors, or molecules acting on DNA damage repair seems feasible but was essentially evaluated on retrospective or prospective studies with a small number of patients. Furthermore, there is considerable heterogeneity among these studies regarding the dose and fractionation of radiation, the dosage of drugs, and the sequence of treatments used. Conclusions: The combination of RT with most targeted therapies for BC appears to be well-tolerated, but these results need to be confirmed in prospective randomized studies.

Safety of cyclin-dependent kinase4/6 inhibitor combined with palliative radiotherapy in patients with metastatic breast cancer

Introduction

Cyclin-dependent kinase (CDK)4/6 inhibitor is a first-line therapy for metastatic ER+/HER2-breast cancer. However, there are limited data on safety of combined radiotherapy (RT) and CDK4/6 inhibition.

Methods

We conducted a retrospective study of women with metastatic breast cancer who received palliative RT within 14 days of CDK4/6 inhibitor use. The primary endpoint was toxicity per Common Terminology Criteria for Adverse Events v5. Secondary endpoints were pain response and local control based on clinical assessment and imaging.

Results

Thirty patients underwent 36 RT courses with palbociclib (n = 34 courses, 94.4%) or abemaciclib (n = 2, 5.6%). RT was delivered before, concurrently or after CDK4/6 inhibitors in 7 (19.4%), 8 (22.2%), and 21 (58.3%) of cases with median 3.5 days from RT to closest CDK4/6 inhibitor administration. Median RT dose was 30Gy (range 8–40.05Gy). Treated sites included brain (n = 5, 11.6%), spine (n = 19, 44.2%), pelvis (n = 9, 20.9%), other bony sites (n = 6, 14.0%) and others (n = 4, 9.3%). No acute grade ≥3 non-hematologic toxicity occurred. No increased hematologic toxicity was attributable to RT with grade 3 hematologic toxicities rates 16.7%, 0%, and 6.7% before, during, and 2 weeks after RT completion. All but one patient (29/30) achieved symptom relief. Local control rates were 94.4%, 91.7% at 6 and 12 months.

Conclusions

The use of RT within 2 weeks of CDK4/6 inhibitors had low acceptable toxicity and high efficacy, suggesting that it is safe for palliation of metastatic breast cancer.

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CDK4/6 inhibitors with endocrine therapy is a preferred first line therapy for HR+, HER2-metastatic breast cancer.

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Limited data exists on safety of combined radiotherapy and CDK4/6 inhibition in patients with metastatic breast cancer.

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This retrospective cohort study included 30 patients who underwent palliative RT with combined CDK4/6 inhibitor use.

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RT within 2 weeks of CDK4/6 inhibitor had low toxicity and high efficacy, supporting its safety in metastatic breast cancer.

Unexpected toxicity of CDK4/6 inhibitor palbociclib and radiotherapy

Background

Cyclin‐dependent kinase (CDK) 4/6 inhibitors have recently been approved for the treatment of hormone receptor–positive and HER2‐negative metastatic breast cancer in association with endocrine therapy in postmenopausal women. Data on the interaction of CDK4/6 inhibition and radiotherapy are scarce, but some studies show unexpected toxicity.

Cases

We report three cases of unexpected severe or prolonged soft tissue, skin, and gastrointestinal toxicity in patients treated with a combination of radiotherapy and the CDK4/6 inhibitor palbociclib.

Conclusion

These cases indicate a possible interaction between radiotherapy and palbociclib. Therefore, we recommend using radiotherapy cautiously when combined with CDK4/6 inhibitors.

Safety of palbociclib concurrent with palliative pelvic radiotherapy: discussion of a case of increased toxicity and brief review of literature

Several cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are indicated in the treatment of metastatic hormone receptor-positive (HR)/ human epidermal growth factor receptor 2 (HER2) negative breast cancer which includes palbociclib, ribociclib and abemaciclib. Pelvic radiation therapy (RT) is often indicated for symptomatic or progressive bone metastasis. There are limited data on concurrent use of CDK4/6 inhibitors with pelvic RT with few retrospective studies in the literature involving a small number of patients. The major side effects of these agents include haematological toxicities, while non-haematological toxicities are less severe. There are concerns for an increased possibility of synergistic toxicity with concurrent use of CDK4/6 inhibitors with pelvic RT. Here we describe an instance of acute grade 3 gastrointestinal toxicity and discuss the relevant literature. A 77-year-old lady treated with palliative conventional RT 30 Gy/ 10 fractions concurrently with palbociclib to left hemipelvis and proximal femur, developed severe pancolitis starting 5 days from last RT. She needed inpatient care for 3 weeks and recovered with mesalamine and supportive care. We also postulate a few strategies that can be adopted in patients receiving palliative RT in such a scenario. The agents should be stopped 1 week before, during and for a time (1 week minimally) after RT. A shorter course of 5 fractions (and ablative RT as indicated) can be considered to minimise treatment gaps. Highly conformal techniques (intensity-modulated radiotherapy/ volumetric-modulated arc therapy) can significantly reduce bowel dose and should be considered in patients with pre-existing GI comorbidities or prior GI toxicity with these agents.

Impact of treatment schedule on the efficacy of cytostatic and immunostimulatory agents

Radiation therapy (RT) and cyclin-dependent kinase 4/6 (CDK4/6) inhibitors mediate poorly overlapping cytostatic and immunostimulatory effects, suggesting that combinatorial regimens may enable supra-additive tumor control. Our preclinical findings demonstrate that administration schedule stands out as a major determinant of efficacy when RT and CDK4/6 inhibitors are combined for breast cancer therapy.