IDO1 has been presented as a novel immune-related gene in oral squamous cell carcinoma (OSCC) in the mRNA sequencing data of the TCGA dataset [20], potentially associated with tumor progression, immune evasion, and suppression, and IDO1 inhibitors have already been used in clinical trials for cancer immunotherapy in other carcinomas [21]. This evidence concerns the gene IDO1 and oral cavity squamous cell carcinoma.