Combination Immunotherapy (Relatlimab/Nivolumab)–Associated Capillary Leak Syndrome: A Case Report

Immune checkpoint inhibitors (ICIs) are the preferred first-line treatment of metastatic melanoma. While dual immunotherapy improves efficacy, it also increases the risk for immune-related adverse events (irAEs). Capillary leak syndrome (CLS) is a rare and potentially serious irAE that can be challenging to recognize. We present a woman with metastatic melanoma who developed dyspnea, peripheral edema, and pleural effusions after 6 cycles of relatlimab–nivolumab. She was diagnosed with secondary CLS, likely triggered by immunotherapy. Treatment with intravenous immunoglobulin led to significant clinical improvement. This case highlights the importance of early recognition and management of rare irAEs such as CLS.