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 anal-ysed 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.(c) 2022 Elsevier B.V. All rights reserved. Radiotherapy and Oncology 177 (2022) 40-45

Automated summary

Through a retrospective analysis of data from 132 consecutive HR+/HER2- breast cancer patients, the study found no significant association between concurrent radiotherapy (RT) and adverse events (AEs) in patients treated with CDK4/6 inhibitors (CDK4/6i). Additionally, RT did not affect the dosage reduction or treatment discontinuation rates of CDK4/6i. The results highlight the safety of this combination therapy.