Further validation through the TIMER2.0 and Xiantao tool indicated that there were significant negative correlations in both online tools between CRABP2 and three checkpoint molecules in breast invasive carcinoma (BRCA), skin cutaneous melanoma (SKCM), stomach adenocarcinoma (STAD) and testicular germ cell tumors (TGCT) (Figs. 1B–1M). This evidence concerns the gene CRABP2 and testicular germ cell tumor.