SAGE1 (Sarcoma Antigen 1) is a cancer/testis antigen normally expressed exclusively in testicular germ cells but aberrantly activated in various human cancers 1. In normal development, SAGE1 is expressed in a subset of post-pubertal germ cells, most likely B spermatogonia, supporting its role in male germ cell development 2. The protein localizes to nuclear bodies and nucleoplasm and functions as part of the integrator complex involved in snRNA 3'-end processing, suggesting a role in RNA metabolism. SAGE1 expression varies significantly across cancer types. It shows high expression in 50% of non-small cell lung cancer samples and serves as an immunogenic target, with specific T-cell receptors demonstrating antitumor efficacy in preclinical models 3. In contrast, SAGE1 is rarely expressed in breast and lung cancers when examined by immunohistochemistry 1. Among digestive tract cancers, SAGE1 is expressed in 33% of esophageal squamous cell carcinomas and their precursor lesions 4, but rarely in colorectal cancers. Clinically, SAGE1 represents a potential immunotherapeutic target due to its cancer-specific expression pattern. In multiple myeloma, SAGE1 functions downstream of the LILRB1-GATA2 pathway, promoting cell proliferation 5. The restricted expression pattern and demonstrated immunogenicity make SAGE1 a candidate for cancer vaccine development and T-cell-based immunotherapies.