Herein disclosed are methods that are prognostic for neoplastic/preneoplastic disease in a subject vertebrate, wherein said disease is associated with a tissue that normally expresses MN, but which MN expression is lost or diminished upon carcinogenesis. Exemplary of the types of preneoplastic/neoplastic diseases subject to the prognostic methods of this invention are those of gastric mucosa, gallbladder, biliary ducts, and ductal cells of duodenal glands. An exemplary prognostic method comprises comparing the level of MN gene expression product in a tissue sample from the affected subject, with the average MN gene expression product level found in analogous preneoplastic/neoplastic tissue samples; an above average MN gene expression product level indicates poorer prognosis for the subject. MN gene expression products useful in the prognostic methods include MN protein, MN polypeptide, and/or MN nucleic acids.