GENETIC INSTABILITY, P53 AND NM23 MUTATION AND CLINICOPATHOLOGICAL FEATURES IN RECTAL-CARCINOMA

Defective DNA mismatch repair proteins fail to correct replication err ors (RERs). These defects may lead to secondary mutation of oncogenes and tumor suppressor genes. Microsatellite instability might be a mark er of such replication errors. Eighteen rectal tumors were examined to evaluate genetic instability in sporadic rectal cancel by PCR. RERs w ere observed in 27.8% of the cases. No significant difference was noti ced between RER+ and RER- patients as far as prognosis, clinicopatholo gical features and p53 gene mutation are concerned. The incidence of n m23 gene mutation was the only statistically significant difference be tween the 2 groups. Three patients with only one altered microsatellit e showed advanced tumor and nm23 gene mutation. Two cases with 5 alter ed microsatellites and nm23 gene mutated are disease-free: in one of t hem the p53 gene was also mutated. Probably more than one altered micr osatellite is necessary to protect from the effects of secondary mutat ions.