| Abstract [eng] |
Lung and head-neck tumours are malignancies with high rates of incidences and deaths in Lithuania and world-wide. The most important risk factor for these malignancies is tobacco smoke. Tobacco smoke contains a mixture of well known carcinogens and procarcinogens, which are shown to induce genetic and epigenetic alterations. In this study, we aimed to determine the frequency and profile of epigenetic (DNA methylation) changes in pathogenesis of tobacco smoke-related lung and head-neck tumours. Tumour supressor genes (TSGs) p16, p14, RARB, RASSF1, MGMT and DAPK were studied by methylation specific PCR and pyrosequencing in lung, head-neck and salivary gland carcinomas (n=212, n=31 and n=36, respectively). Also, scrapes of oral mucosa from subjects with no cancer indication (n=11) and histologically normal salivary gland tissues (n=19) were analysed. MGMT protein expression was analysed by immunohistochemistry in 287 of salivary gland speciments. In lung tumours, promoter hypermethylation was detected in 20.8% of p16, 31.1% of RARB, 28.9% of RASSF1, 15.1% of MGMT and 19.8% of DAPK1 gene. The prevalence of p16 hypemethylation was significantly higher in males than females (p=0.018), squamous cell carcinomas than adenocarcinomas (p=0.025). Hypermethylation of ≥1 gene promoter is associated with TP53 mutations (p=0.027). Methylation index and the frequency of p16 promoter methylation in neversmokers exposed to second-hand tobacco smoke is similar to indices observed in tumours from smokers. In head-neck tumour scrapings, promoter hypermethylation was detected in 23% of p16, 20% of p14, 19% of RASSF1, 20% of RARB, and 50% of MGMT gene. Hypermethylation in ≥1 gene promoter is higher in specimens obtained from smokers than neversmokers (p=0.047). In salivary gland carcinomas and histologically normal tissues promoter hypermethylation was detected in 27.8% and 15.8%, respectively. Epigenetic changes in gene MGMT promoter are associated with loss of MGMT protein expression (p=0.021). The loss of MGMT protein expression in salivary gland tumours is characteristic for patients with poor prognosis (high grade, certain histologic types, lymph node involved tumours). Our study contributes to understanding of tobacco smoke induced molecular alterations in lung and head-neck tumours. Hypermethylation of TSG promoters reflect the harmful effect of tobacco smoke or second-hand tobacco smoke exposure. Analysis of promoter hypermethylation of TSGs in oral scrapings from high risk subjects (smokers) may be a valuable tool for an early prediction of head-neck cancer risk. In salivary gland carcinomas, hypermethylation of gene MGMT promoter causes the loss of MGMT protein expression. This alteration is significant in pathogenesis of salivary gland tumours. |
