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. ICI rechallenge after severe irAEs is debated.

Case: We describe a case of a 65-year-old male with R/M-SNSCC who is currently in remission with pembrolizumab monotherapy. He developed high-grade pneumonitis during the course of treatment warranting ICI discontinuation but has since tolerated full-dose pembrolizumab for 10 months now which is holding his disease stable. Our approach toward restarting full-dose pembrolizumab was by monitoring the patient's response to an initial low dose of pembrolizumab with concomitant oral steroid immunosuppression to control CIP.

Conclusion: Clinicians should weigh the risk-to-reward ratio of ICI rechallenge after improvement of high-grade CIP, particularly for selected patients with aggressive tumors such as R/M-SNSCC and prior treatment response. Under close monitoring, ICI resumption at a low dose and assessing patient tolerance with concomitant immunosuppression may be a reasonable approach to reintroducing ICI after high-grade CIP in these patients.