Black Hairy Tongue After Immune Checkpoint Inhibitors in NSCLC: A Case Report and Review of the Literature

•Immune checkpoint inhibitors (ICIs) are associated with the development of unique immune-related adverse events (irAEs), which emerged primarily during post-marketing surveillance. Oral irAEs have already been reported, with the most common manifestations being mucositis and xerostomia. It has been suggested that a T-cell activation, similar to that observed in autoimmune conditions, may play a role.•Here, we report a case of black hairy tongue (BHT) in a patient receiving first-line pembrolizumab for advanced non–small-cell lung cancer (NSCLC). Although the BHT was symptomatic for burning mouth and dysgeusia, ICI use was continued due to its clinical and radiological benefit, which persisted for a long time.•BHT is characterized by hypertrophy and lengthening of the filiform papillae. Despite being a rare benign condition, it can often result in a significant burden on quality of life.•Many predisposing factors have been described, and cancer patients represent a population particularly at risk. Based on the temporal association and excluding possible alternative causes, we proposed that, in our patient, BHT was likely ICI related through the development of xerostomia, which represents a key factor in BHT pathogenesis.•To the best of our knowledge, this is the first report of BHT after ICI use, suggesting that it may represent an atypical oral irAE. To date, the oral irAEs have not been well explored, and further studies are needed to elucidate the underlying mechanisms and possible associations with anti-tumor responses, with significant implications on prognosis and quality of life. In the present context, our case emphasizes the need to remain vigilant for atypical and new irAEs.