ESTRO 2025 - Abstract Book

S590

Clinical - Breast

ESTRO 2025

in the RT+P group. Among the 31 patients who continued adjuvant pembrolizumab, 8 received RT followed by sequential adjuvant pembrolizumab, and 23 received concomitant pembrolizumab with RT. All but one underwent normofractionated RT: 72 received breast irradiation, 40 received chest wall irradiation, and 82 received additional nodal irradiation. The RT tolerance profile was similar in the RT + P and RT alone groups (table 1). No differences in Grade 1–2 toxicities (radiodermatitis, edema, esophagitis) were identified between the groups. Three patients (2.7%) developed grade ≥3 toxicity (1 case of radiation dermatitis in the RT alone group and 2 in RT+P group). Persistent grade 1–2 radiodermatitis at six months was observed in 9 patients (8.2%) (6 in RT only and 3 in RT+P group including 1 with pembrolizumab concurrent). One case of grade 2 radiation-induced pneumonitis was reported in the RT+P group vs none in the RT alone group. No cardiac toxicity was observed. Among patients who received adjuvant pembrolizumab, only one grade 3 radiodermatitis was reported in the pembrolizumab concomitant group compared to none in the sequential group (table 2).

Conclusion: This study suggests that adjuvant RT can be safely administered to patients receiving pembrolizumab without excessive radiation-induced toxicity. The schedule of adjuvant pembrolizumab administration does not seem to affect radiotherapy toxicity.

Keywords: Immunotherapy, Radiotherapy, Toxicity