Abstract: Herein disclosed is a novel oncogene named MN or alternatively MN/CA IX. The MN protein has been determined to be the first tumor-associated carbonic anhydrase isoenzyme that has been described. Abnormal expression of the MN gene is shown to signify oncogenesis, and diagnostic/prognostic methods for pre-neoplastic/neoplastic disease to detect or detect and quantitate such abnormal MN gene expression, e.g., immunoassays and nucleic acid hybridization assays, are provided. Also disclosed are methods to treat pre-neoplastic/neoplastic disease involving the MN gene and protein, e.g., methods comprising the use of MN-specific antibodies, conjugated or unconjugated to cytotoxic agents, and the use of MN antisense nucleic acids.