HIGH-FREQUENCY OF P16 (CDKN2 MTS-1/INK4A) INACTIVATION IN HEAD AND NECK SQUAMOUS-CELL CARCINOMA/

The tumor suppressor gene p16 (CDKN2/MTS-1/INK4A) can be inactivated b y multiple genetic mechanisms, We analyzed 29 invasive primary head an d neck squamous cell carcinomas (HNSCC) for p16 inactivation with immu nohistochemistry utilizing a new monoclonal antibody (mAb), DCS-50. p1 6 staining of the primary lesions was correlated with genetic analysis including: (a) detailed microsatellite analysis of markers at the p16 locus to detect homozygous deletion; (b) sequence analysis of p16; an d (c) Southern blot analysis to determine the methylation status of th e 5' CpG island of p16. Twenty-four of 29 (83%) head and neck squamous cell carcinoma tumors displayed an absence of p16 nuclear staining us ing immunohistochemistry. Of these 24 tumors, we found that 16 (67%) h arbored homozygous deletions, 5 (21%) were methylated, 1 displayed a r earrangement at the p16 locus, and 1 displayed a frameshift mutation i n exon 1, These data suggest that: (a) inactivation of the p16 tumor s uppressor gene is a frequent event in squamous cell carcinomas of the head and neck; (b) p16 is inactivated by several distinct and exclusiv e events including homozygous deletion, point mutation, and promoter m ethylation; and (c) immunohistochemical analysis for expression of the p16 gene product is an accurate and relatively simple method for eval uating p16 gene inactivation.