The present invention discloses that the normal melanogenic gene, gp75 gene, encodes a gene product, a 24 amino acid peptide of ORF3, which is processed to an antigenic cancer peptide recognized by T lymphocytes. The cancer peptide of the invention derived from ORF3 is recognized by cancer antigen specific T lymphocytes as a tumor rejection antigen. The products of this gene are promising candidates for immunotherapeutic strategies for the treatment and diagnosis of patients with cancer.