Aim-To study p53 expression in relation to proliferative status in normal and nondysplastic, dysplastic and malignant lesions of the oral mucosa. Method-The standard avidin-biotin complex (ABC) immunohistochemical staining method was used to study the expression of p53 and Ki67 on frozen sections of oral leukoplakias and carcinomas.Results-Of the leukoplakia and carcinoma samples, 70% expressed p53 in over 5% ofcells. In normal mucosa less than 5% of cells expressed p53. The proliferation index, as assessed by expression of Ki67, was highest in the malignant lesions (43%) and lowest in normal mucosa (11% Of the pre-malignant lesions, oral leukoplakia has greatest relevance in the study of the biology of carcinogenesis because the oral cavity is easily accessible for clinical examination4 and also because it has a multistage carcinogenesis pathway and of the concept of field cancerisation.' The oral carcinogenesis pathway can be broadly classified histopathologically into normal, non-dysplastic, dysplastic, carcinoma-insitu, and invasive carcinoma.4 Molecular biological studies on oral cancer have identified several genetic aberrations in the cells during various tumour stages.6 7Mutations in the p53 tumour suppresser gene are the most common genetic changes in humans cancers and are regarded as early events in carcinogenesis.8"-In pre-malignant and malignant oral lesions, alterations in p53 expression have been reported both at protein and DNA levels.12-18 As cancer is characterised by uncontrolled cell proliferation, markers of proliferation, such as Ki67 and proliferating cell nuclear antigen, have been studied extensively in neoplastic lesions.'9 Ki67 is a nuclear antigen which is present in the perichromosomal region during mitosis and seems to be a non-histone protein, representing a new class of cell cycle maintaining proteins.20 Studies on proliferation markers in lesions of the oral mucosa have shown that expression of Ki67 is correlated with the severity of the lesion. [21][22][23][24] Studies on the relation between p53 and the proliferation index in various malignancies, including lesions of the oral mucosa, have been reported previously.25"-Our aim was to elucidate the relation, if any, between expression of p53 and Ki67 in normal, non-dysplastic, dysplastic, and neoplastic lesions of the oral mucosa and to determine whether these markers have potential as early indicators of malignancy.
MethodsFifty tissue samples, five of normal oral mucosa, 30 of leukoplakia and 15 of invasive carcinoma, were studied. Demographic details were recorded for all patients and included age, sex and whether they used tobacco products. Only those patients with oral leukoplakia and carcinoma at non-keratinising sites of the oral cavity were included. A 4 mm punch biopsy specimen was collected from each patient, immediately snap frozen and stored in liquid nitrogen. Cryostat sections, 5 ,um thick, were cut from each biopsy specimen and fixed in cold acetone. One section from each biopsy
