GAGE4 encodes a cancer-testis antigen recognized by autologous cytolytic T lymphocytes on melanoma cells 1. As a member of the GAGE gene family, GAGE4 is presented by HLA class I molecules and recognized by CD8+ T cells, making it a promising immunotherapy target 1. GAGE4 expression is largely restricted to cancer tissues and normal tissues including spermatogonia and placental cells, with minimal expression in differentiated somatic tissues 1. In pediatric rhabdomyosarcoma, GAGE4 is expressed in approximately 16% of tumors as part of a multi-gene cancer-testis antigen profile 1. GAGE4 shows differential transcription activity across breast cancer subtypes, with enhanced expression observed in non-metastatic compared to metastatic breast cancer 2. GAGE4 is also overexpressed in paclitaxel and doxorubicin-resistant ovarian and breast cancer cell lines, suggesting potential involvement in chemotherapy resistance mechanisms 3. Given its tumor-restricted expression pattern and immunogenic properties, GAGE4 represents a candidate antigen for active specific immunotherapy in cancer patients expressing this gene.