The results showed that in BLCA (P < 0.001), BRCA (P < 0.001), COAD (P < 0.05), and THCA (P < 0.001), PCSK9 was positively correlated with PDCD1, CD274, and CTLA4 but negatively correlated in HNSC (P < 0.05) and testicular germ cell tumor (TGCT) (P < 0.01). Here, CTLA4 is linked to testicular germ cell tumor.