Fatal toxicity induced by anti-PD-1 immune checkpoint inhibitor in thymic epithelial tumor.

A standard treatment for advanced thymic epithelial tumors (TETs) after initial treatment remains unavailable to date. Targeted immune checkpoint inhibitors (ICIs) of the programmed cell death-1 (PD-1) pathway may produce objective responses in TETs, notably thymic carcinoma. Findings of clinical trials suggested ICIs are a practical choice. However, the risk of severe immuno-related adverse events is higher in TETs. Concerning histologic subtypes, thymomas are more frequently associated with autoimmune disorders than carcinomas, so close monitoring is needed for thymomas. In this article, we describe four cases of fatal toxicity caused by anti-PD-1 therapy in TETs. Four patients with metastatic thymomas or carcinoma difficult to treat with first-line standard chemotherapy were treated with the anti-PD-1 drug pembrolizumab or sintilimab. The association of PD-1 inhibitors with a high proportion of severe immuno-related adverse events in TETs necessitates attentive monitoring during treatment.