P53 MUTATIONS IN GASTRIC AND COLORECTAL CANCERS IN TEXAS HISPANICS VERSUS ANGLOS

Gastric cancer is more than twice as common in Hispanics as in Angles in Texas, while colorectal cancer is almost twice as common in Angles as Hispanics. To test the hypothesis that mutations in the p53 tumour suppressor gene are involved in these differences, we examined 131 gas tric and 138 colorectal cancers from Hispanic and Angle patients from South Texas and Mexico using immunohistochemistry (IHC) as a screening assay for p53 mutations. The fraction of p53 positive cases was not s ignificantly different in gastric cancers from Hispanics compared to A ngles (43% versus 61%, respectively, p=0.13) or in colorectal cancer ( 57% versus 58%, respectively, p=1.0), suggesting that p53 mutations ar e not involved in causing the different incidences of these cancers in these populations. In addition, the types of p53 mutations arising in gastric tumours from Hispanic patients were consistent with those rep orted in gastric tumours in other populations. Sequencing of mutations in five gastric cancers revealed two G: C to A: T transitions, two A: T to G: C transitions and one complex deletion. In contrast with find ings in studies in other tumour types, neither stage nor survival was associated with p53 positive staining by IHC in either gastric or colo rectal tumours in this study. Positive p53 immunostaining was associat ed with the diffuse histological subtype in gastric carcinoma (p=0.05) and high histological grade in colorectal carcinoma (p=0.04).