Aberrant Methylation of RASSF1A Closely Associated with HNSCC, a Meta-Analysis

Head and neck cancer is the sixth most common cancer worldwide accounting for approximately 6% of all newly diagnosed malignancies. HNSCC makes up over 90% of head and neck cancer, and commonly arises from the mucosal lining in this region1. Epidemiological data demonstrates that heavy smoking and alcohol consumption contribute to HNSCC tumorigenesis2. Human papillomavirus (HPV) can also implicate the increased incidence of HNSCC in the United States3. Despite the advances in therapy, the overall survival rates of HNSCC have not improved significantly over the past several decades and more than 50% of patients have experienced local relapse and distant metastasis4. Early diagnosis of HNSCC might improve its prognosis, but it is usually not detected in the early stages of HNSCC. Therefore, the efforts to identify novel molecular predictors for HNSCC are instrumental for early diagnosis in the early stage of cancer development. DNA methylation of cytosine-guanosine dinucleotides (CpG) islands within the promoter region of genes is an alternative mechanism of gene inactivation to gene deletion or mutation. Teschendorff5 observed that invasive cancers displayed increased DNA methylation at the risk CpG sites in contrast to normal tissue, but lower levels in contrast to pre-cancerous lesions. This revealed that aberrant DNA methylation of risk CpG loci was prior to the onset of cancer, indicating that epigenetic diversity in normal cells increased the risk of cancer. Aberrant DNA methylation is frequently considered to be critical in the early stage of cancer development, including HNSCC6. Previous studies had investigated the association between hypermethylation of tumor suppressor genes and HNSCC and evaluated the value of them as potential biomarkers of HNSCC7,8,9,10,11,12. RASSF1A, a kind of tumor suppressor gene, is one of eight isoforms of RASSF1 which is involved in cell cycle control, microtubule stabilization, cellular adhesion and motility as well as apoptosis13. Epigenetic inactivation of RASSF1A by hypermethylation is originally described in lung and breast cancer14. Since then, it has emerged that RASSF1A is one of the most frequently hypermethylated genes so far described and was reported as a prognostic indicator in renal cell carcinoma, non-small cell lung cancer, neuroblastoma, endometrial cancer and breast cancer15,16,17,18,19,20,21. Furthermore, hypermethylation of RASSF1A within promoter CpG islands is frequently observed in the HNSCC cell lines22. All of these findings indicate that RASSF1A might play an important role in the development of HNSCC. To date, a number of studies have investigated the association between aberrant methylation of RASSF1A and HNSCC through a comparison of the methylation prevalence of RASSF1A between cancerous tissues and controls. However, the obtained results of these studies are inconclusive and inconsistent23,24. Therefore, we conducted a meta-analysis of 12 published studies to conclude the association.