Supplementary Material for: Sequential Multiple-Organ Immune-Related Adverse Events During and After Pembrolizumab Therapy in Triple-Negative Breast Cancer: A Case Report

Immune checkpoint inhibitors (ICIs) are an important component of triple-negative breast cancer (TNBC) treatment, and the KEYNOTE-522 regimen has established pembrolizumab combined with chemotherapy, as the standard of care. While ICIs improve outcomes, they can also induce immune-related adverse events (irAEs), affecting diverse organs. However, renal, pancreatic, and ocular toxicities are rare, and there have been few reports of sequential multi-organ irAEs in breast cancer. This case study describes a 63-year-old woman with stage IIA TNBC who was treated with the KEYNOTE-522 regimen. During neoadjuvant therapy, she developed fever, malaise, and mild laboratory abnormalities. Her symptoms progressed to acute kidney injury and elevated pancreatic enzymes. She was diagnosed with immune-related acute interstitial nephritis and pancreatitis and improved promptly with high-dose corticosteroids. After tapering immunosuppression, the patient developed Pneumocystis jirovecii pneumonia. Subsequently, she suffered bilateral anterior uveitis consistent with an immune-related ocular event. Surgical resection revealed a pathological complete response (pCR), and she remains under surveillance. This case included three distinct irAEs affecting the kidney, pancreas, and eye. Each occurred at a different time point, including after discontinuation of immunotherapy. The opportunistic infection that she developed during steroid therapy emphasizes the need for prophylaxis in patients requiring prolonged immunosuppression. This case underscores the importance of multidisciplinary management and long-term vigilance for delayed and multi-organ irAEs in TNBC patients treated with ICIs.