Evaluation of hypermethylated tumor suppressor genes as tumor markers in mouth and throat rinsing fluid, nasopharyngeal swab and peripheral blood of nasopharygeal carcinoma patient

The purpose of our study was to evaluate the frequency of hypermethylated tumor suppressor genes (TSGs) in peripheral blood, mouth and throat (M&T) rinsing fluid and nasopharyngeal (NP) swabs of nasopharyngeal carcinoma (NPC) patients. Six normal NP tissues, 43 M&T rinsing fluid, 37 NP swabs and 43 peripheral blood from healthy non-smokers and non-drinkers without a family history of NPC, and 30 NPC tumors and their matched body fluid were analyzed for the presence of hypermethylated p15, p16, Ras association domain family 1 (RASSF1A), E-cadherin, and death-associated protein kinase (DAPK) by methylation-specific PCR. Sequencing analysis was carried out on selected NPC tumors and body fluid samples. Twenty-nine (97%) tumors displayed methylation in at least 1 of the 5 genes. The methylation frequencies were 80% for p15, 77% for DAPK, 67% for RASSF1A, 53% for E-cadherin and 33% for p16. The frequency range of aberrant methylated genes in the body fluids were NP swabs (17-63%) and M&T rinsing fluid (17-50%). Methylation was found in <20% of peripheral blood for each respective gene. Methylation was, however, detected in 1 M&T rinsing fluid in which the primary tumor showed methylation free for RASSF1A. Five healthy individuals exhibited methylation for DAPK, or RASSF1A, or p15 in their body fluid samples. All body fluid samples of healthy controls showed methylation free for E-cadherin and p16. Epigenetic change is found frequently in NPC and the high detection rate in body fluids suggest its potential application in non-invasive screening of NPC or detection of residual carcinoma after treatment.