Firstly, the CYP27A1 expression level in various tumors and normal samples was compared by TIMER data, and results indicated that CYP27A1 was decreased in bladder urothelial carcinoma (BLCA), cholangio carcinoma (CHOL), colon adenocarcinoma (COAD), head and neck squamous cell carcinoma (HNSC), kidney chromophobe (KICH), liver hepatocellular carcinoma (LIHC), LUAD, lung squamous cell carcinoma (LUSC), prostate adenocarcinoma (PRAD), rectum adenocarcinoma (READ), thyroid carcinoma (THCA), and uterine corpus endometrial carcinoma (UCEC) compared to normal samples. The gene discussed is CYP27A1; the disease is head and neck squamous cell carcinoma.