P16INK4a point mutations and promoter hypermetylation in bronchial preneoplastic lesions

The aim of this study was to determine p16INK4a point mutations and promoter hypermethylation in tumour cells and bronchial preneoplastic lesions in 32 surgically resected lungs due to primary squamous cell carcinoma. P16 point mutations were detected in 1 (3%) and promoter hypermethylation in 12 (31%) of 32 squamous cell carcinomas. The status of p16 was further characterized in 38 premalignant lesions including squamous metaplasias without dysplasia, squamous metaplasias with mild, moderate and severe dysplasias and 4 carcinomas in situ. No p16 point mutations have been found in premalignant or CIS lesions. Methylation of p16 was detected in 1 of 8 (12.5%) cases of squamous metaplasias without dysplasia, in 1 of 10 (10%) cases of squamous metaplasias with mild dysplasia, in 1 of 9 (11%) cases of squamous metaplasia with moderate dysplasia and in 2 of 7 (28.5%) cases of severe dysplasias, as well as in 1 of 4 (25%) carcinomas in situ. This investigation indicates that P16INK4a supressor gene point mutations are rather late event and inactivation of this gene by promoter hypermethylation is early and likely critical in bronchial cancerogenesis.