Loss of heterozygosity on the short arm of chromosome 9 without p16 gene mutation in gastric carcinomas.

A putative tumor suppressor gene, p16 (MST1; multiple tumor suppressor 1/CDK4I; cyclin-dependent kinase 4 inhibitor), was isolated and mapped on the short arm of chromosome 9 (9p). The significance of p16 mutations in gastric tumorigenesis was examined by assessing p16 mutations as well as loss of heterozygosity (LOH) on 9p in 13 gastric adenomas and 45 adenocarcinomas. LOH on 9p (IFNA; alpha-interferon locus) was detected in 22% (5/23 informative cases) of differentiated adenocarcinomas, 10% (1/10) of undifferentiated carcinomas and none (0/6) of the adenomas. Although we found a sequence polymorphism at the second position of codon 99 (CGC/CAC) of the p16 in one gastric adenoma patient, no somatic mutations were detected in any of the gastric adenomas or adenocarcinomas. These results suggest that p16 mutations probably do not contribute to gastric tumorigenesis. However, these data suggest that another tumor suppressor gene on 9p (near the IFNA locus) may contribute to the progression of differentiated adenocarcinoma of the stomach.