Hypermethylation of RASSF1A and BLU tumor suppressor genes in non-small cell lung cancer: implications for tobacco smoking during adolescence.

The putative tumor suppressors RASSF1A and BLU are mapped adjacent to one another on chromosome 3p21.3, a region frequently deleted in lung cancer. These genes are often inactivated by promoter hypermethylation, but the association of this inactivation with clinical features of the disease or with carcinogen exposure has been poorly studied. Early age starting smoking has been hypothesized as an independent risk factor for lung cancer, and mechanistically, adolescence may constitute a critical period for tobacco carcinogen exposure. To study the relationship of tobacco smoke exposure with hypermethylation of RASSF1A and BLU, methylation-specific PCR was performed on a case series study of incident, surgically resected non-small cell lung cancer (NSCLC), and the prevalence of this alteration was examined in relation to clinical and exposure information collected on the patients. Hypermethylation of the RASSF1A promoter occurred in 47% (83/178) and of the BLU promoter in 43% (68/160) of NSCLC tumors examined. There was no significant association between methylation of these 2 genes, but methylation of either of these genes tended to occur more often in the adenocarcinoma (AC) histology compared to squamous cell carcinoma (SCC). Controlling for pack-years smoked, age, gender and histology, starting smoking under age 18 was significantly related to RASSF1A methylation [prevalence ratio (PR) = 1.6, 95% confidence interval [CI] = 1.1-2.3]. These results indicate that starting smoking under age 18 is an independent risk for RASSF1A hypermethylation, thus identifying a molecular alteration related to the epidemiologic effect of teenage smoking as a lung cancer risk. (c) 2004 Wiley-Liss, Inc.