Expression of cyclin dependent kinase inhibitor p21waf1/cip1 in premalignant and malignant oral lesions: relationship with p53 status.

p21waf1/cip1 protein, an inhibitor of cyclin dependent kinases, is a critical downstream target in the p53-specific pathway of growth control, and can also be induced by p53 independent pathways in relation to terminal differentiation. p21waf1 is also a putative tumour suppressor. Hence, we sought to determine whether this protein is abnormally expressed during betel- and tobacco-related oral oncogenesis. The aim was to determine whether a correlation exists between the expression profile of p21 and clinicopathological parameters of the patients, as well as with their p53 status. Immunohistochemical analysis showed that the expression of p21 protein in premalignant lesions was consistently elevated in the superficial, differentiated cells of the epithelium, while overexpression of the p53 tumour suppressor gene was observed in the basal proliferating layers of the epithelium. Our study demonstrated that p21 overexpression is associated with differentiation in proliferating dysplasias and squamous cell carcinomas (SCCs). The expression of p21 and p53 proteins was observed in 11/25 premalignant lesions. In 7 of these 11 cases, a heterogenous pattern of expression of p21 and p53 was observed. Four of these 11 premalignant and 30/51 malignant lesions showed concordant expression of both p21 and p53 proteins. The discordant p21 +/p53- phenotype was observed in 4/25 premalignant lesions and 5/51 oral SCCs. The p21-/p53+ phenotype was observed in 5/25 premalignant lesions and 7/51 oral SCCs. These results suggest that induction of p21 occurs by both p53 dependent and independent mechanisms during oral tumorigenesis.