Koos Boeve

126 Chapter 7 reported [17]. Other promising markers associated with N-status in OSCC were RAB25 and S100A9 hypermethylation and expression levels, markers selected using a genome wide methylation assay [20][Clausen, S100A9, manuscript in prep]. These molecular biomarkers (cortactin, cyclin D1, FADD, RAB25 and S100A9) have been reported as potential prognostic and predictive tumor markers in early stage OSCC, but have not been studied in relation to SLNB staged patients. The aim of this study was to analyze the additional clinical value of combining classical prognostic factors (tumor stage and tumor infiltration depth) withmolecular tumor biomarkers in order to select patients for a watchful waiting or SLNB procedure as neck strategy using preoperative tumor biopsies of early stage OSCC patients who underwent neck staging using the SLNB procedure. MATERIAL AND METHODS Patients and treatment Patients diagnosed with cT1-2N0 and pT1-2 OSCC (7 th TNM classification), treated by primary surgical resection and neck staging with SLNB between 2008 and 2017 were selected for analysis. These patients were treated in the University Medical Center Groningen (UMCG) (n = 101) and the Medical Center Leeuwarden (MCL) (n = 12). Most of these patients (n = 91) were part of a clinical study assessing the accuracy of the SLNB procedure [7]. Clinical and histopathological data were retrospectively collected from the electronical patient files (Table 1). Pathological reports are standardized in our centers and contain data on tumor infiltration depth, tumor pattern of invasion, extranodal extension, perineural invasion, lymphovascular invasion and N-status. In case of missing histopathological data, tumors or lymph nodes were reassessed by a pathologist (BvdV). Eighty-seven of the 113 tumors were suitable for biomarker analysis (see tissue microarray construction below). Twenty- six (30%) of these 87 patients had a positive SLN and received a modified radical neck dissection in a second operation. SLNB negative patients (70%) had a clinical follow-up of the neck. Four SLN negative patients were diagnosed with a regional recurrence without local disease during follow-up (false negatives) after 8, 9, 18 and 22 months. Ten patients received postoperative radiotherapy, which was combined with chemotherapy in two patients indicated by involved surgical resection margins, multiple positive lymph nodes or extranodal extension. The median follow-up time was 35 months (IQR 20-49 months). Thirteen (15%) patients deceased during the follow-up of which two died as a result of the OSCC.