A novel gene (designated 121P1F1) and its encoded protein, and variants thereof, are described wherein 121P1F1 exhibits tissue specific expression in normal adult tissue, and is aberrantly expressed in the cancers listed in Table I. Consequently, 121P1F1 provides a diagnostic, prognostic, prophylactic and/or therapeutic target for cancer. The 121P1F1 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 121P1F1 can be used in active or passive immunization.