A new gene—MN—and proteins/polypeptides encoded therefrom are disclosed. Recombinant nucleic acid molecules for expressing MN proteins/polypeptides and recombinant proteins are provided. Expression of the MN gene is disclosed as being associated with tumorigenicity, and the invention concerns methods and compositions for detecting and/or quantitating MN antigen and/or MN-specific antibodies in vertebrate samples that are diagnostic/prognostic for neoplastic and pre-neoplastic disease. MN-specific antibodies are disclosed that can be used diagnostically/prognostically, therapeutically, for imaging, and/or for affinity purification of MN proteins/polypeptides. The invention still further concerns antisense nucleic acid sequences that can be used to inhibit MN gene expression.