Immune-related adverse events among patients with early-stage triple-negative breast cancer treated with pembrolizumab plus chemotherapy: real-world data from the Neo-Real/GBECAM 0123 study.

Background: Pembrolizumab combined with neoadjuvant chemotherapy is the standard of care for stage II-III triple-negative breast cancer (TNBC) based on the KEYNOTE-522 trial. However, 13 % of patients experienced immune-related adverse events (irAEs) of grade ≥3 in the trial. This study aims to describe patterns of irAEs in a real-world scenario during treatment with pembrolizumab for early-stage TNBC.

Methods: Patients treated with neoadjuvant pembrolizumab plus chemotherapy across ten Brazilian cancer centers were evaluated in the Neo-Real/GBECAM0123 study. This analysis focuses on irAE evaluation, including time to onset, management, and association between irAEs and pathological complete response (pCR).

Results: A total of 368 patients were included. Overall, 31 % of patients (n = 114) presented with any grade irAEs. Most of irAEs (72.8 %) occurred during the neoadjuvant phase while 28.1 % happened during the adjuvant period. The most frequent irAEs were endocrine (12.8 % of the entire cohort), cutaneous (7.6 %) and gastrointestinal (7.1 %). A total of 50 patients (13.6 %) experienced grade ≥3 irAEs, predominantly gastrointestinal (32 %). 58 patients (56 %) needed corticosteroids. Immunotherapy rechallenge was possible in 53 % of the cases; permanent discontinuation of pembrolizumab was necessary for 16 %. No significant association was observed between irAEs and clinic-pathologic features nor pCR status.

Conclusions: In this real-world analysis, we observed a similar incidence of irAEs as reported in the KEYNOTE-522 trial. Most patients experienced resolution of their irAEs, but some required permanent discontinuation of pembrolizumab. Additionally, there were lasting dysfunctions, particularly endocrine, demanding lifelong support. Careful monitoring and management of these events are essential.