Melanoma-Associated Antigen 4 (MAGE-A4) is a member of the melanoma-associated antigen (MAGE) family of proteins and is expressed in lung cancer, breast cancer, bladder cancer, hepatocellular carcinoma, esophageal cancer, oral squamous cell carcinoma, gastrointestinal stromal tumors and gastric cancer, urothelial carcinoma, colorectal cancer, desmoid tumors, osteosarcoma, soft tissue sarcoma, synovial sarcoma, T cell leukemia/lymphoma, endometrial cancer, cervical cancer, ovarian cancer, vulvar cancer, uterine carcinosarcoma, salivary gland tumors, melanoma, and head and neck cancer. The gene discussed is MAGEA4; the disease is osteosarcoma.