2879 - Outcomes and Toxicity of Concurrent CDK46 Inhibitor and Adjuvant Radiation Therapy in Early Breast Cancer
Presenter(s)
Y. Song1, H. Wu1, Y. Zhang1, H. Tu2, and Q. Lin1; 1Department of Radiation Oncology, Shanghai Tenth People’s Hospital of Tongji University, Shanghai, 200072, China, 2Radiation Oncology Center, Chongqing University Cancer Hospital, Chongqing, China
Purpose/Objective(s): The European Society for Radiotherapy and Oncology (ESTRO) has indicated that CDK4/6 inhibitor (CDK4/6i) and concomitant radiotherapy (RT) during adjuvant locoregional RT for breast cancer should be investigated in the context of a clinical trials or prospective registration cohorts. This recommendation received a 100% consensus agreement, though it was based largely on evidence from metastatic settings, lacking controlled studies, case reports, or expert opinions specifically addressing concurrent CDK4/6i use with postoperative locoregional radiotherapy in early breast cancer. In this study we would like evaluate the safety especially for Grade= 3 hematologic toxicities and radiotherapy interruptions happened of concurrent use of radiotherapy and CDK4/6 i (abemaciclib/ ribociclib/ dalpiciclib) in patients with hormone-receptor positive (HR+), stage II-III, node-positive, early breast cancer.
Materials/Methods: Toxicity was assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events version 5.0 (NCI-CTCAE V5.0). The primary safety endpoints were Grade= 3 hematologic toxicities and radiotherapy interruptions.
Results: A total of forty-two patients received adjuvant radiotherapy concurrently with CDK4/6 inhibitors (CDK4/6i) between December 2021 and August 2024. The final follow-up time was December 2025. Among all patients, 30 (71.4%) were treated with Abemaciclib, 6 (21.4%) with ribociclib and 3(7.1%) with dalpiciclib concurrent with radiotherapy. Grade= 3 hematologic toxicities were frequently observed during radiotherapy, especially for leukopenia, which occurred in 5 patients (17%) in the abemaciclib group, 6 (66.7%) in the ribociclib group, and 2 (66.7%) in the dalpiciclib group. Radiotherapy interruption occurred in 4 patients (14.3%) in the abemaciclib group whereas 4 patients (44.7%) in ribociclib group and 2 (66.7%) in dalpiciclib group because of Grade=3 leukopenia. 2 interruptions because of COVID-19 infection in abemaciclib group. Only 2patients (4.8%) happened grade = 3 dermatitis, 2 patients with grade = 3 diarrhea, no other grade = 3 reaction happened when concurrent with radiotherapy and CDK4/6i. At the time of analysis, 2 patients had disease recurrence.
Conclusion: Abemaciclib and radiotherapy appears to be better tolerated than ribociclib or dalpiciclib combined with radiotherapy. Although high grade hematologic toxicities were often observed, but most patients treated with abemaciclib did not modify their treatment during radiotherapy.