The present invention is directed to compositions of matter useful for the diagnosis and treatment of tumor in mammals and to methods of using those compositions of matter for the same. TAT113 polypeptides comprising the amino acid sequence of SEQ ID NO: 2 are disclosed. Antibodies that bind TAT113 polypeptides, including monoclonal, chimeric, humanized, single chain, and other antibodies, and fragments thereof, are disclosed. Methods of identifying antibodies that bind epitopes bound by such antibodies, including the antibodies produced by hybridoma cell lines disclosed in the application, are provided, wherein the ability of one antibody to block the binding of another antibody to a TAT113 polypeptide indicates that one antibody binds to an epitope bound by the other antibody. Methods of diagnosing the presence of a tumor in a mammal using such antibodies are disclosed, wherein detection of the formation of a complex between an antibody and a protein in a test sample is indicative of the presence of a tumor in said mammal. Methods of inhibiting the growth of a cancer cell that expresses a protein comprising the amino acid sequence of SEQ ID NO: 2, are disclosed, where the binding of the antibody to the protein inhibits the growth of the cell. Methods of inhibiting the growth of a cancer cell include methods wherein the antibody binds to the epitope bound by an antibody produced by a disclosed hybridoma cell line.