Real-world immune-related adverse events in patients with early triple negative breast cancer who received pembrolizumab.

1099 Background: The addition of pembrolizumab to chemotherapy (KEYNOTE-522 regimen) in high risk early triple negative breast cancer (TNBC) has improved clinical outcomes. However, this treatment can result in immune-related adverse events (irAEs) involving any organ and in some cases, life-long toxicities or even death. This retrospective study describes real-world patterns of irAEs in patients (pts) with early TNBC who received pembrolizumab at two academic centers. Methods: We evaluated irAEs in pts with stage II-III TNBC from MD Anderson Cancer Center and Lyndon B Johnson diagnosed between January 2018 and May 2023 who received neoadjuvant pembrolizumab plus chemotherapy. We excluded those enrolled on clinical trials. We utilized ASCO irAE and CTCAE v5 guidelines for toxicity grading. Logistic regression assessed the effect of clinical variables on irAEs, adjusting for covariates. Results: We identified 233 pts with a median age of 51 ± 12 years; 62% with stage II and 35% with stage III TNBC; 25% were Hispanic/Latino, 21% non-Hispanic Black and 42% were non-Hispanic White. In total, 80 pts (34%) developed 100 separate irAEs (94 with definite and 6 with possible/probable attribution). The most common irAEs were endocrine (52%) followed by gastrointestinal (23%). Grade ≥ 3 irAE occurred in 26 instances, with the most common being gastrointestinal (13 instances). A fatal irAE occurred in 2 pts where both were colitis. A total of 26 irAEs resulted in hospitalization, 45 required systemic steroids, and 15 required additional immunosuppressive therapy. Most (66) irAEs were unresolved at last follow up, although the majority had improved to grade 1 (37/66) and 32 patients discontinued pembrolizumab early due to irAEs. No clinical factor (race, stage, tumor grade, age, body mass index) was associated with development of an irAE. Conclusions: In this real-world diverse population, we identified a similar rate and severity of irAEs as reported in the KEYNOTE-522 trial. Hospitalizations occurred in 26% of irAEs while most developed persistent immune toxicity. Gastrointestinal irAEs were more common compared to KEYNOTE-522 reported data. Research is needed to better predict and mitigate the burden of irAEs and to improve the long-term survivorship care of pts with early TNBC pts who receive pembrolizumab. Table: see text