GPR137 and gastric adenocarcinoma: According to Gene Expression Profiling Interactive Analysis (GEPIA) database, GPR137 expression was significantly up-regulated in stomach adenocarcinoma (STAD, accounting for around 90–95% of all GC [21]) tissue samples (T, Tumor) in comparison with control group (N, Normal) (Fig. 1A), and the elevated expression of GPR137 was further validated by immunohistochemistry staining, showing the increased GPR137 expression in STAD samples than matched controls (adjacent normal tissues, Fig. 1B,C).