Immune-Related Adverse Events in Breast Cancer Patients Who Received Neoadjuvant Chemotherapy with Pembrolizumab: What Needs to Be Managed Before Surgery

<b>Background:</b> Pembrolizumab is a novel immunotherapy agent that improves oncological outcomes for various cancers. This study aimed to investigate immune-related adverse events (irAEs) that occurred after neoadjuvant chemotherapy (NAC) with pembrolizumab for triple-negative breast cancer (TNBC) and to identify fatal irAEs that should be addressed before surgery under general anesthesia. <b>Methods:</b> A total of 82 patients who received NAC with pembrolizumab followed by surgery were reviewed based on their medical records. All irAEs during NAC were evaluated and classified into nine categories: systemic, dermatologic, central nervous, musculoskeletal, endocrine, gastrointestinal, respiratory, ocular, and hematologic systems. Clinicopathologic characteristics were compared between patients with and without irAEs, and cases in which surgery was postponed due to irAEs were reviewed and analyzed. <b>Results:</b> Fifty-nine patients (72.0%) experienced irAEs after NAC with pembrolizumab. The mean NAC period was 140.3 days, with a 39.8-day window to surgery. The most common and second most common irAEs were myalgia (n = 33, 40.3%) and skin rash/dermatitis (n = 31, 37.8%), respectively. There were 1 case (1.2%) of adrenal insufficiency and 16 cases (19.5%) of thyroid dysfunction as irAEs. In 6 cases (7.3%), surgery was postponed due to irAEs [systemic (n = 2, 33.3%); endocrine (n = 3, 50.0%); increased transaminase (n = 1, 16.7%)], with a mean delay of 64.5 days (range, 57-80 days). <b>Conclusions:</b> IrAEs following NAC with pembrolizumab in TNBC were diverse and included those severe enough to affect the timing of surgery under general anesthesia. These irAEs should be monitored continuously during NAC and detected early to address them when they occur.