Real world feasibility of combining pembrolizumab with radiotherapy in early triple negative breast cancer

Real-world data on the feasibility and potential interaction of concurrent immunotherapy with radiation therapy (RT) remains limited. Herein, we investigated the safety profile of adjuvant pembrolizumab with concomitant RT given with curative intent in operable triple negative breast cancer (TNBC) patients. We conducted the INT 54/24 study to prospectively collect data from patients with operable TNBC treated with neoadjuvant chemotherapy plus pembrolizumab followed by surgery and adjuvant pembrolizumab with concomitant RT. A total dose of 40.05 Gy delivered in 15 fractions was prescribed to the breast or chest wall, with regional nodes and tumor bed boost administered as clinically indicated. The study endpoint was to assess both acute toxicity (as per Radiation Therapy Oncology Group scale) and the rate of discontinuation of RT and/or pembrolizumab. Among the 10 female patients with TNBC enrolled between January and October 2024, the median age was 58 years (range, 27–68 years). Seven patients (70%) presented with stage II disease, with all cases classified as grade 3. A median of 8 (range 4–9) cycles of neoadjuvant pembrolizumab were prescribed. Before RT, patients received a median of 3 (range 2–4) cycles of adjuvant pembrolizumab. Severe acute toxicity occurred in 2 cases. Specifically, G4 myositis led to permanent discontinuation of adjuvant pembrolizumab in one case, whereas G3 electrolyte imbalance caused definitive RT interruption and temporary discontinuation of adjuvant pembrolizumab in the second case. Only 2 patients experienced G2 skin erythema, with no treatment discontinuation. Our findings show that concurrent RT and pembrolizumab is feasible with manageable toxicities, providing valuable support for clinicians in real-world practice beyond the selective context of clinical trials.