Herein disclosed is a novel oncogene named MN or alternatively MN/CA IX. 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. 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, anti-idiotype antibodies thereto, and anti-anti-idiotype antibodies, and the use of MN antisense nucleic acids. Further disclosed are methods to identify and block MN binding site(s) and identify MN protein partners(s).