Koos Boeve

144 Chapter 8 ABSTRACT Background: The high local recurrence and/or second primary tumor rate of 20-30% in patients with oral squamous cell carcinoma (OSCC) is partly caused by residual tumor cells of the first primary tumor and the presence of precancerous epithelium that has not (yet) clinically manifested. Since OSCC cells are shed into the oral cavity, the detection of tumor-specific DNA methylation markers in saliva could be a tool for the early detection of local recurrences or second primary tumors of OSCC. The aim of this explorative study was to identify and validate new methylation markers to detect OSCC cells in saliva. For that purpose, we investigated molecular biomarkers methylated in OSCC and not in normal cells from a genome-wide methylation screening analysis using MethylCap-Seq analysis of 12 OSCCs compared to controls. In addition, we selected 4 markers reported to be methylated in saliva by others ( EDNRB, HOXA9, NID2 and TIMP3). Results: Using our OSCC methylome, seven genomic locations representing six genes ( C11orf85 , CMTM2 , FERMT3 , KCNA5 , SIPA1 and TBX4 ) were identified that were significantly hypermethylated in tissues of OSCC compared to DNA from controls. QMSP analysis using saliva from OSCC patients compared to non-cancer controls of similar age or younger age, revealed only a difference for KCNA5 methylation (respectively p = 0.003 and p = 0.001). Moreover, when KCNA5 was combined with other markers, the combination with TIMP3 revealed a 100% diagnostic potential in detecting OSCC patients compared to non-cancer controls of similar age using saliva. Conclusions: In this explorative study we identified several new OSCC-specific methylation markers with a high sensitivity and high negative predictive value for the detection of OSCC in saliva. Two methylation markers ( KCNA5 and TIMP3 ) might be useful for early detection of local recurrence or second primary tumors in saliva cells of OSCC patients. A larger prospective study should be done to confirm the clinical relevance of these two markers.