PAEP (progestagen-associated endometrial protein), also known as glycodelin, is a 28-30 kDa glycoprotein synthesized primarily in reproductive tissues that plays critical roles in fertilization and immune regulation 1. The protein exists as multiple glycoforms—glycodelin-A, -S, -F, and -C—with distinct biological activities determined by tissue-specific glycosylation patterns 1. Endometrium-derived glycodelin-A is temporally expressed during the luteal phase and inhibits sperm-egg binding while exerting potent immunosuppressive effects 12. In contrast, seminal plasma glycodelin-S maintains spermatozoa in an uncapacitated state and lacks contraceptive activity 1. PAEP expression is hormonally regulated, increasing significantly during the secretory phase following progesterone exposure 3. Beyond reproduction, emerging evidence indicates PAEP functions as a tumor mutational burden-related immune gene in clear cell renal cell carcinoma, where its overexpression correlates with poor prognosis 4. PAEP knockdown in ccRCC cell lines suppressed proliferation, migration, and invasion while promoting apoptosis, potentially through PI3K/Akt/NF-κB pathway inhibition 4. As a lipocalin family member 5, PAEP represents a novel link between reproductive physiology and cancer biology, suggesting potential therapeutic applications in both gynecological and oncological contexts.