Concurrent Trastuzumab Deruxtecan and Radiation Therapy in HER2-positive and HER2-low Metastatic Breast Cancer

The combination in patients with HER2-positive and HER2-low metastatic breast cancer (MBC) of Concurrent Trastuzumab Deruxtecan (T-DXd) and Radiation Therapy (RT) is not enough studied. We conducted a retrospective study including patients treated between 11/2020 and 01/2024. Patients with HER2-positive and HER2-low MBC who received concurrent T-DXd and RT were identified. Data on patient demographics, treatment regimens, radiation doses, toxicity profiles, efficacy, and treatment discontinuations were collected. The toxicities were graded using CTCAE V5.0. Population of 33 patients with HER2-positive and HER2-low MBC who underwent concurrent T-DXd&RT, were studied. The median follow-up (FU) was 14 months. There were 39.4 partial remissions and 9.4 attained complete remission. In addition, 39.4% experienced stable disease, and 12.1% faced disease progression necessitating a change in therapy. Safety assessment revealed that acute toxicities were mainly associated with systemic treatment. Survival analysis showed 11 deaths (33.3%) during the FU period, with a median overall survival of 26 months and median progression-free survival of 12 months. The combination of T-DXd with RT in demonstrates promising efficacy with a manageable safety profile. Further studies are warranted to fully elucidate the potential synergistic effects of this treatment regimen and its impact on patient outcome.