A specific region of chromosome 10 (10q23.3) has been implicated by series of studies to contain a tumor suppressor gene involved in gliomas, as well as a number of other human cancers. One gene within this region was identified, and the corresponding coding region of the gene represents a novel 47 kD protein. A domain of this product has an exact match to the conserved catalytic domain of protein tyrosine phosphatases, indicating a possible functional role in phosphorylation events. Sequence analyses demonstrated the a number of exons of the gene were deleted in tumor cell lines used to define the 10q23.3 region, leading to the classification of this gene as a tumor suppressor. Further analyses have demonstrated the presence of a number of mutations in the gene in both glioma and prostate carcinoma cells. Methods for diagnosing and treating cancers related to this tumor suppressor, designated as TS10q23.3, also are disclosed.