MSMB (microseminoprotein beta) encodes prostate secretory protein 94 (PSP94), an immunoglobulin superfamily protein synthesized by prostate epithelial cells and secreted into seminal plasma 1. The gene demonstrates tissue-specific expression with high activity in prostate-derived cells but negligible expression in non-prostate tissues 2. Mechanistically, MSMB expression is regulated through androgen response elements and androgen receptor signaling pathways 1. The rs10993994 polymorphism, located near MSMB, represents a major prostate cancer risk locus. Risk allele (T) carriers produce significantly reduced MSMB expression—over 100-fold lower than the protective C-allele—and show approximately 25% increased prostate cancer risk per T allele 34. This polymorphism acts as a trans-eQTL affecting SNHG11 expression through MSMB-mediated regulation 4. Disease relevance extends beyond prostate cancer: MSMB serves as a marker gene identifying signet ring cell carcinoma and moderately/poorly differentiated gastric adenocarcinoma 5, and MSMB expression is associated with a transcriptional resistance program in HER2-positive esophagogastric cancer 6. Clinically, decreased PSP94 levels correlate with increased prostate cancer susceptibility, suggesting a protective mechanism possibly involving tumor suppression or antifungal activity 3. The tissue-specific MSMB promoter shows promise for targeted prostate cancer gene therapy applications 2.