MDM-2 PROTEIN EXPRESSION IN NASOPHARYNGEAL CARCINOMAS - COMPARATIVE-STUDY WITH P53 PROTEIN EXPRESSION

Aims - To investigate the immunohistochemical expression of MDM-2 prot ein in comparison with that of p53 protein in nasopharyngeal carcinoma s. Methods - Formalin fixed, paraffin wax embedded tissue from 59 case s of nasopharyngeal carcinoma was stained by immunohistochemistry for MDM-2 and p53 proteins. Results - The tumours were divided histologica lly into seven cases of keratinising nasopharyngeal carcinoma (KNPC), 14 cases of non-keratinising nasopharyngeal carcinoma (NKNPC), and 38 cases of undifferentiated nasopharyngeal carcinoma (UNPC). MDM-2 nucle ar expression was observed in 0/7 KNPC, 1/14 NKNPC, and 11/38 UNPC. p5 3 nuclear expression was observed in 1/7 KNPC, 2/14 NKNPC, and 15/38 U NPC. Parallel MDM-2 and p53 expression was found in 12 cases (11 UNPC and one NKNPC). Discordant MDM-2-/p53 + expression was found in six ca ses (four UNPC, one NKNPC, and one KNPC), and absence of expression of both proteins in the remaining 41 cases. Conclusions - Expression of MDM-2 and p53 proteins may be associated with the level of tumour cell differentiation in nasopharyngeal carcinoma. Simultaneous expression of MDM-2/p53 in a proportion of UNPC suggests that MDM-2 protein may b e responsible for stabilisation of p53 protein in these cases, in view of the previous demonstration of the p53 gene in germ line configurat ion. This could be important in the pathogenesis of these cases, since MDM-2 may deregulate the p53 dependent growth suppressive pathway. Di scordant MDM-2-/p53 + expression in a few cases of nasopharyngeal carc inoma may reflect stabilisation of p53 protein by other proteins, or p 53 mutations unable to activate MDM-2.