P16(INK4) GENE-MUTATIONS ARE RELATIVELY FREQUENT IN AMPULLARY CARCINOMAS

A high incidence of gene mutations or deletions of p16(INK4), a cell c ycle regulator which inhibits the activity of cyclin-dependent kinase 4/cyclin D complex and blocks the G1-to-S transition, has been reporte d in pancreato-biliary tract cancers. In order to investigate p16(INK4 ) gene alterations in sporadic ampullary carcinomas, 17 sporadic ampul lary carcinomas were examined. After histological diagnosis, DNA sampl es extracted separately from both cancerous and normal paraffin-embedd ed tissues were investigated. Loss of heterozygosity (LOH) was investi gated utilizing 3 microsatellite markers on 9p21-22, and a mutational analysis was performed by cloning and sequencing. LOH was observed in 3 cases (17.6%) and somatic mutations with retention of heterozygosity were found in 7 cases (41.2%). Of note was that two mutations resulte d in truncated incomplete proteins and one was a point mutation at the consensus site in the conserved ankyrin repeats, which would be cruci al for function. Although two-hit inactivation was not evident in any of the mutation cases and further investigation would be needed to elu cidate the role of altered p16(INK4), these results suggest that the p 16(INK4) gene mutations are relatively frequent and its inactivation m ight be important in ampullary carcinogenesis.