Low prevalence of expression of p53 oncoprotein in oral carcinomas from Sri Lanka associated with betel and tobacco chewing.

Overexpression of p53 oncoprotein has been demonstrated in a wide range of human malignancies. We have examined the p53 expression amongst 38 Sri Lankan subjects with histologically confirmed oral squamous cell carcinomas. The mean age of the subjects was 59.4 years and betel chewing with tobacco was the most common habit (84%) with a high percentage of patients smoking (63%). Buccal mucosa was the most frequently affected site (68%) with a high proportion (79%) of well differentiated carcinomas. p53 expression was examined by standard immuno-histochemical methods on frozen sections using monoclonal antibodies PAb 1801, 240 and 421. Only 4 (11%) carcinomas showed nuclear reactivity mostly in random clusters of basal neoplastic cells. The low frequency of p53 expression could be due to deletion of both alleles or to premature truncated protein products due to nonsense mutations resulting in loss of antibody recognition sites. Alternatively the much lower prevalence than reported by others could be due to differences in aetiological agents and/or genetic predisposition of this population.