The protein expression level of PNPO was low in LUSC (n = 4), TGCT (n = 3), PESC (penis squamous cell carcinoma, n = 5), ESCA (n = 5), STAD (n = 5), and READ (n = 3), which also has no significant difference (Supplementary Figures S3A–F). Here, PNPO is linked to squamous cell carcinoma of penis.