br Acknowledgements br Introduction Laryngeal cancers
Introduction Laryngeal cancers are the most frequent cancers of the head and neck region and their occurrence is strongly associated with the exposure to cigarette smoke and the consumption of strong alcohols. Almost all laryngeal cancers are squamous cell carcinomas. Usually the disease is diagnosed at a late stage and the major risk of failure is the development of a local relapse. It has been proven that molecular markers (e.g. p53 status assessment) could be applied for the prediction of the risk for a local relapse. One of the explanations of the value of such molecular markers comes from the field cancerization theory of carcinogenesis, presented more than fifty years ago by Slaughter et al. Environmental carcinogens, such as polycyclic aromatic hydrocarbons or nitrosamines present in cigarette smoke, induce molecular changes in a large field of mucosa cells which predispose for cellular carcinogenesis. The acquirement of additional defects leads to the formation of cancer cells. Because a large field is molecularly predisposed to tumorigenesis, cancer cells can be formed in distant sites of the affected mucosa. So far, evidence has accumulated that the field defect in head and neck squamous cell carcinomas (HNSCC) is associated with the occurrence of aberrant genetic changes.2, 4 In laryngeal carcinomas the field cancerization phenomenon is associated with such genetic aberrations as, for example, the loss of heterozygosity of 13q14 and 13q34. The latest findings indicate that the field defect can be also associated with aberrant changes in the epigenome.5, 6 The hypermethylation of DNA is a key epigenetic mechanism for the silencing of many genes responsible for TCS JNK 6o regulation, inflammatory and stress response, DNA repair and apoptosis. Hypermethylation of certain genes, particularly tumor suppressor genes, is known to be associated with the inactivation of various pathways involved in tumorigenesis. Different environmental factors are able to modulate the epigenetic information. It is widely accepted that the aberrant DNA methylation changes can be induced by both cigarette smoke and alcohol. Alcohol consumption and smoking induced the hypermethylation of p15 in the upper respiratory tract cells, while the hypermethylation of MGMT, p16 and DAPK was associated with tobacco-chewing induced oral cancers. A correlation was also found between cigarette smoking and the hypermethylation of CDH1, RARbeta and FHIT.10, 11 Alcohol consumption was associated with the methylation of APC, p14, p16, MGMT, RASSF1A and hMLH1. Since alcohol and tobacco are the major risk factors for the development of laryngeal squamous cell carcinomas (LSCC), one can predict the frequent occurrence of the methylome aberrations in LSCC patients. There are a few reports indicating that changes in the profile of DNA methylation can be observed in both the HNSCC tumor samples and the adjacent margins. Also, it has been shown that DNA methylation analysis could be applied as a biomarker for the determination of the resection area and for prognosis. So far, only a small number of papers have been published with respect to the assessment of the characteristic changes in the DNA methylation profile in LSCC. Current findings show frequent hypermethylation of p16 or MLH1.14, 15 Metastasizing laryngeal cancers were characterized by the aberrant methylation of CDH1. In the study of Dikshit et al. the hypermethylation of p16, MGMT, DAPK or CDH1 did not correlate with the occurrence of second primary tumors or patients mortality. The aim of this study was to assess the methylation status of a panel of genes (RARbeta, RASSF1A, FHIT, GSTP1, MGMT, VHL and DAPK) in laryngeal squamous cell carcinomas and paired normal mucosa samples and correlate it to the clinicopathological characteristics of the patients. The genes selected for the analysis play an important role in the effective regulation of cellular proliferation and apoptosis (VHL, FHIT, RARbeta, RASSF1A, DAPK, HIN-1), DNA repair (MGMT) or xenobiotic metabolism (GSTP1). The genetic loss of function of these genes is frequently observed in HNSCC cancers. The choice of the genes was also based on the available information about the correlation of their methylation with either the exposure to cigarette smoke or alcohol consumption in other tumor types.9, 10, 11, 12 We found frequent gene hypermethylation in both the cancer cells and the normal epithelium samples which indicates the occurrence of an epigenetic field defect in laryngeal tumors.