Antibodies and molecules derived therefrom that bind to novel STEAP-1 protein, and variants thereof, are described wherein STEAP-1 exhibits tissue specific expression in normal adult tissue, and is aberrantly expressed in the cancers listed in Table I. Consequently, STEAP-1 provides a diagnostic, prognostic, prophylactic and/or therapeutic target for cancer. The STEAP-1 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 STEAP-1 can be used in active or passive immunization.