Pembrolizumab induced remission of recurrent and metastatic sinonasal squamous cell carcinoma after overcoming checkpoint-inhibitor pneumonitis: A case report and literature review.

Background: For programmed death-ligand-1 (PD-L1) positive recurrent and metastatic head and neck squamous cell carcinoma (R/M-HNSCC), KEYNOTE-048 and KEYNOTE-040 clinical trials recently approved pembrolizumab monotherapy as first-line treatment. However, recurrent and metastatic sinonasal squamous cell carcinoma (R/M-SNSCC) was excluded from these clinical trials and treatment reports of immune-checkpoint inhibitor (ICI) in R/M-SNSCC are sparse. Immune-related adverse events (irAEs) are known to occur during ICI treatment and some of these such as checkpoint-inhibitor pneumonitis (CIP) can be fatal.