CGB5 (chorionic gonadotropin subunit beta 5) encodes the β5 subunit of human chorionic gonadotropin (hCG), a placental hormone with emerging roles beyond reproduction. 1 In gastric cancer, CGB5 is significantly upregulated compared to adjacent normal tissue and promotes tumorigenesis through enhanced proliferation, migration, and invasion while suppressing apoptosis. 1 2 CGB5 expression independently predicts poor overall survival and recurrence-free survival specifically in advanced gastric cancer stages. 2 In ovarian cancer, CGB5 promotes vasculogenic mimicry formation and tumor growth via luteinizing hormone receptor (LHR) signaling activation. 3 Pan-cancer analysis reveals CGB5 is upregulated in liver, lung, and gastric cancers, correlating with altered immune infiltration patterns and involvement in immunodeficiency and CD8 T-cell signaling pathways. 4 Beyond cancer, CGB5 promoter variants protect against recurrent miscarriage in North European populations. 5 CGB5 also shows diagnostic potential as a preeclampsia biomarker. 6 These findings establish CGB5 as a multi-system biomarker with cancer-promoting functions mediated by immune modulation and hormone signaling, offering therapeutic and diagnostic applications.