Infrequent Somatic Mutation of the MTS1 Gene in Primary Bladder Carcinomas

We examined a candidate tumor suppressor gene on chromosome 9p21, MTS1/CDK4I (multiple tumor suppressor 1/cyclin‐dependent kinase 4 inhibitor), which has been found to be mutated frequently in cell lines derived from bladder carcinomas, for somatic mutations in 39 primary bladder cancers by means of SSCP (single‐stranded conformational polymorphism) and DNA sequencing. Mutations were detected in two of these carcinomas; one was a 61‐base deletion and the other a 1‐base deletion. In both cases the homologous allele was missing, indicating that “two‐hit”mutation of the MTS1 gene had taken place in these tumors. The results indicated that inactivation of the MTS1 gene is likely to be a contributing factor in some, but not the majority of, bladder cancers.