Safety and Tolerability of Concurrent Radiotherapy and Sacituzumab Govitecan in Metastatic Breast Cancer

Objectives: Sacituzumab govitecan, an anti-TROP2 antibody-drug conjugate, is approved for metastatic triple-negative breast cancer (TNBC) from the second-line setting and for hormone receptor-positive/HER2-negative (HR+/HER2−) breast cancer from the third line. Radiotherapy is frequently required in metastatic settings for symptom control, but its combination with sacituzumab govitecan has not been formally evaluated. This study aims to assess the safety and tolerability of concurrent sacituzumab govitecan and radiotherapy in metastatic breast cancer patients. Methods: This retrospective, single-center study included all metastatic breast cancer patients who received sacituzumab govitecan and underwent external beam radiotherapy (EBRT) at Institut Curie. Clinical and pathologic data, treatment details, toxicities graded per CTCAE v5.0, and survival outcomes were analyzed. Overall survival (OS) was estimated using the Kaplan-Meier method. Results: Thirteen patients were included, with a mean age of 54 years. The majority (61.5%) had TNBC. A total of 19 metastatic sites were irradiated, including 10 brain and 9 bone metastases. No radiation-induced toxicity was observed, and no patients required treatment interruption. Grade 3 to 4 toxicities were limited to neutropenia (15.4%). The median OS from radiotherapy completion was 6 months, with a 6-month OS rate of 45.1% and a 12-month OS rate of 16.9%. Conclusions: The concurrent administration of sacituzumab govitecan and radiotherapy appears well tolerated, with no increased toxicity. This combination may be feasible in metastatic breast cancer patients when clinically indicated. Further studies with larger cohorts are necessary to confirm these findings.