XAGE3 (X antigen family member 3) is a cancer/testis antigen located on chromosome X that functions as a protein-binding molecule implicated in malignant transformation. XAGE3 belongs to a superfamily of GAGE-like cancer/testis antigens 1 and is frequently expressed in various cancers while remaining silent in most normal tissues except placenta 1. In glioblastoma, XAGE3 is expressed in 44% of cases with no expression in normal brain tissue 2. Notably, glioblastoma patients expressing 3-4 cancer/testis antigens including XAGE3 demonstrate significantly better overall survival rates (P=0.017) and mRNA positivity for multiple antigens serves as an independent prognostic factor 2. Similarly, in high-grade ovarian serous adenocarcinoma, loss of X chromosome X leads to XAGE3 upregulation, correlating with aggressive tumor behavior and poor clinical outcomes 3. XAGE3 shows enhanced expression in metastatic breast cancer compared to non-metastatic disease 4, and appears as part of a validated autoantibody biomarker panel (CEACAM1-DPPA2-DPPA3-MAGEA4-SRC-TPBG-XAGE3) for pancreatic ductal adenocarcinoma detection with 85% AUC 5. These findings position XAGE3 as a potential immunotherapy target and cancer diagnostic biomarker across multiple malignancies.