A novel gene (designated 84P2A9) and its encoded protein is described. While 84P2A9 exhibits prostate and testis specific expression in normal adult tissue, it is aberrantly expressed multiple cancers including prostate, testis, kidney, brain, bone, skin, ovarian, breast, pancreas, colon, lymphocytic and lung cancers. Consequently, 84P2A9 provides a diagnostic and/or therapeutic target for cancers, and the 84P2A9 gene or fragment thereof, or its encoded protein or a fragment thereof used to elicit an immune response.