Low p53 protein expression in salivary gland tumours compared with lung carcinomas

Fifty-one salivary gland tumours (23 pleomorphic adenomas, 5 Warthin's tumours, 12 mucoepidermoid carcinomas, 7 adenoid cystic carcinomas, 3 undifferentiated carcinomas and 1 acinic cell tumour) and 27 lung carcinomas (18 squamous cell carcinomas) were analysed immunohistochemically for the expression of p53 nuclear phosphoprotein. Eight out of 51 (16%) salivary gland tumours were p53 positive. Three of these were benign and 5 malignant. All 3 benign salivary gland tumours were pleomorphic adenomas and expressed only occasional nuclear positivity with less than 1% of tumour cells positive. Of the 5 p53-positive malignant tumours, 3 were mucoepidermoid carcinomas and 2 undifferentiated carcinomas. The malignant salivary gland tumours expressed more than 1% of positive nuclei in every case. Seventeen lung carcinomas were p53 positive (63%). Thirteen of these were squamous cell carcinomas, 3 were adenocarcinomas and 1 small cell lung carcinoma. The results show that mutations of the p53 gene may be infrequent in salivary gland tumours when compared with lung carcinomas. The relatively indolent course of some histological types of malignant salivary gland tumours could be associated with the preservation of the non-mutated p53 gene in most of these tumours. The presence of p53 positivity in some pleomorphic adenomas might, on one hand, suggest that p53 gene alterations are also present in these tumours; on the other hand, the accumulation of the p53 protein in these tumours might also be due to some unknown mechanism, not necessarily related to p53 gene mutation.