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

## TL;DR

This study examines side effects from pembrolizumab and chemotherapy in breast cancer patients, highlighting the need for monitoring to avoid surgery delays.

## Contribution

The study identifies specific immune-related adverse events that can delay surgery in breast cancer patients treated with pembrolizumab and chemotherapy.

## Key findings

- 72% of patients experienced immune-related adverse events after treatment.
- Thyroid dysfunction and liver toxicity were the main causes of surgery delays.
- Surgery was postponed in 7.3% of cases, with an average delay of 64.5 days.

## Abstract

Pembrolizumab combined with chemotherapy is increasingly used before surgery in triple-negative breast cancer, but it can cause immune-related side effects. In this study, most adverse events were mild, yet some—such as thyroid dysfunction and liver toxicity—delayed surgery. Careful monitoring during treatment is essential to prevent unnecessary postponement and ensure safe surgical care.

Background: 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. Methods: 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. Results: 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). Conclusions: 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.