DNA Content and Methylation of p16, DAPK and RASSF1A Gene in Tumour and Distant, Normal Mucosal Tissue of Head and Neck Squamous Cell Carcinoma Patients

Long-term survival of head and neck squamous cell carcinoma (HNSCC) patients has not improved significantly during the last 20 years and recurrent disease is frequently observed. In this study, the potential presence of pre-malignant cells or rare malignant cells at the time of diagnosis in HNSCC was investigated. Fifty-nine biopsies obtained from 41 HNSCC patients were analysed. Eighteen of these biopsies were normal mucosal tissue, located at least 5 cm from the tumour margin. DNA content and DNA methylation of p16, DAPK and RASSF1A was examined. Thirty-nine out of 41 (95%) tumour biopsies showed p16 methylation and 21 (51%) of them displayed aneuploidy. Of 18 distant normal mucosal biopsies, 6 (33%) of these showed evidence of aneuploidy and 15(83%) of them showed methylated p16 genes. Among paired samples, the highest frequencies of DNA methylation were found in tumours with aneuploidy. Regardless of DNA content, methylation at DAPK, RASSF1A or p16 were found in the corresponding distant mucosal biopsies. The cells with abnormal DNA content or DNA methylation in mucosal tissue were not detected clinically or by pathological macroscopic and microscopic examination. Thus, distant mucosal tissue DNA content and DNA methylation analyses in combination with histopathology will provide a better prognostic base for the evaluation and treatment of HNSCC patients.