Overall, the expression of PCSK9 was higher in tumor samples than in normal samples among most tumor types, including breast invasive carcinoma (BRCA) (P < 0.001), cervical squamous cell carcinoma (CESC) (P < 0.05), colon adenocarcinoma (COAD) (P < 0.001), esophageal carcinoma (ESCA) (P < 0.001), head and neck squamous cell carcinoma (HNSC) (P < 0.001), liver hepatocellular carcinoma (LIHC) (P < 0.001), rectum adenocarcinoma (READ) (P < 0.001), stomach adenocarcinoma (STAD) (P < 0.001), thyroid carcinoma (THCA) and uterine corpus endometrial carcinoma (UCEC) (P < 0.001) (Fig. 1A). The gene discussed is PCSK9; the disease is head and neck squamous cell carcinoma.