CTAG was initially cloned from an esophageal squamous cell carcinoma cDNA expression library by immunoscreening with autologous patient's serum. CTAG mRNA is expressed in a proportion of human cancers in a lineage-nonspecific fashion, whereas its expression in normal tissues is restricted to testis and ovary only. This expression pattern suggests that the CTAG product (NY-ESO-1) is an aberrantly activated tumor antigen and can potentially be an antigenic target for tumor vaccination. In the present study, we isolated human genomic clones of CTAG and established its genomic organization. By somatic cell hybrid studies and fluorescence in-situ hybridization, we localized this gene to chromosome Xq28, a region that also contains members of MAGE, a gene family that encodes several immunogenic tumor antigens with the characteristic cancer/testis expression pattern.