We previously reported some cancer testis antigens, especially for MAGE genes, to be expressed in a relatively high population of gastro-intestinal and breast cancers. TRAG-3 (Taxol resistant associated gene-3) may be another cancer testis antigen; however, its expression has still not been fully studied. The TRAG-3 expression was evaluated in a total of 57 cancer cell lines and 322 cancer samples of gastrointestinal and breast cancers by RT-PCR. TRAG-3 was expressed in 23/57 (40%) of the cell lines: the highest expression was found in gastric cancer (6/9: 67%), followed by esophageal (13/28: 46%), colon (3/11: 27%) and liver (1/4: 25%) cancers. In clinical samples, the expression was the highest in esophageal cancer (32/58: 55%), followed by liver (13/50: 26%), bile duct (5/27: 19%), gastric (5/50: 10%), breast (5/50: 10%) and colon (2/87: 2.3%) cancers. The TRAG-3 expression significantly correlated with the expression of MAGE-3 in esophageal cancer (p<0.05). As the TRAG-3 gene is located on Xq28, which is the same locus as the MAGE gene family, we found a frequent synchronous expression pattern with TRAG-3 and MAGE-3 in esophageal cancer.