MDM2/p53 co-expression in oral premalignant and malignant lesions: potential prognostic implications

The expression of MDM2 protein in betel and tobacco related oral malignancies in Indian population, its relationship to clinicopathological parameters and p53 protein expression was investigated. Sixty five oral squamous cell carcinomas (SCCs), 33 premalignant lesions (leukoplakia) and 30 normal oral tissues were assessed by immunohistochemical analysis. MDM2 protein was overexpressed in 51/65 (78%) oral SCCs and 17/33 (52%) premalignant lesions; 11/23 hyperplastic lesions and 6/10 dysplastic lesions. mdm2 gene amplification is an infrequent event in oral tumorigenesis. Elevation in the level of MDM2 protein not only in oral SCCs but also in premalignant lesions suggests that altered MDM2 expression is an early even in the pathogenesis of oral neoplasia. The hallmark of the study was the significant association of MDM2 expression with the p53 protein accumulation in 16/33 (49%) oral premalignant lesions (p = 0.001) and 39/65 (60%) malignant lesions (p = 0.021), suggesting an active role for MDM2 in binding and inactivating p53 in oral tumorigenesis. Further, significant association of MDM2/p53 co-expression was observed with advanced tumour stage (p = 0.0009), as well as lymph node metastasis (p = 0.0325) features associated with aggressive tumour behaviour and poor prognosis. Discordant MDM2+/p53-phenotype was observed in 12/65 (18%) oral SCCs suggesting a p53-independent role for MDM2 in the pathogenesis of a subset of oral carcinomas. In conclusion, alterations in MDM2 and p53 expression are early events likely to be involved in preinvasive stages in oral tumorigenesis and may be indicative of a 'gain of function' phenotype with more aggressive characteristics.