A novel gene 273P4B7 and its encoded protein, and variants thereof, are described wherein 273P4B7 exhibits tissue specific expression in normal adult tissue, and is aberrantly expressed in the cancers listed in Table I. Consequently, 273P4B7 provides a diagnostic, prognostic, prophylactic and/or therapeutic target for cancer. The 273P4B7 gene or fragment thereof, or its encoded protein, or variants thereof, or a fragment thereof, can be used to elicit a humoral or cellular immune response; antibodies or T cells reactive with 273P4B7 can be used in active or passive immunization.