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The origin and neoplastic potential of gastric epithelial polyps remains an area of great interest, and treatment choices are a topic of controversy. This report describes a patient diagnosed with three concurrent hyperplastic gastric polyps that were studied for genetic alterations. The polyps were investigated for alterations in the K-ras oncogene and the p53 tumor suppressor gene and for p21WAF1/Cip1 and MDM2 protein overexpression. In addition, loss of heterozygosity at several loci that are frequently involved in human cancer was analyzed, microsatellite instability, a hallmark of the "mutator" phenotype, was determined, and Epstein-Barr virus infection was investigated. All separate areas from the three independent polyps harbored the same activating point mutation in codon 12 of the K-ras oncogene, indicating a clonal origin. DNA sequence alterations in p53 were not found, although high p53 protein levels could be shown by immunohistochemistry in areas of carcinoma within the largest polyp. No alterations in any of the other molecular markers were observed. The results strongly favor a clonal origin of the three independent gastric polyps and support the notion that these hyperplastic polyps may carry a risk for malignancy.