Koos Boeve

185 General discussion and future perspectives Neck staging in OSCC using molecular biomarkers: cortactin as important driver of metastasis As described more extensively in chapter 1, many cellular processes, such as cell motility, determine the metastatic potential of a tumour cell [68,77]. Epigenetic or genetic alterations of genes with a key-role in cell migration are reported as prognostic for lymph node status [68,78]. A review andmeta-analysis from2015 analysed 11q13 chromosome amplification as promising molecular tumour marker for lymph node status in OSCC and found that CCND1 (one of the genes of that amplicon) and overexpression of its corresponding protein cyclin D1 was a prognostic marker [79]. In chapter 6 [80] we analysed the clinical value of CCND1 amplification and the overexpression of three proteins from three major oncogenes ( CTTN / cortactin, CCND1 /cyclin D1 and FADD) located at the 11q13 amplicon in a well-defined cohort of early stage tongue and FOM OSCC with neck staging using the END procedure. All these biomarkers showed promising NPVs for the detection of occult metastasis: CCND1 copy number 83% and expression of cyclin D1 84%, FADD 81% and cortactin 80% [80]. In chapter 7 we found that cortactin was predictive for SLN status in small and superficial tumours (7 Th TNM pT1 and a tumour infiltration depth <4 mm) with a 92% NPV of early stage OSCC patients with neck staging using the SLNB procedure. Cortactin is the protein encoded by the CTTN gene (also known as EMS1 ), which is one of the genes located at the 11q13 chromosome [79,81,82]. 11q13 amplification is detected in 46% (range 13-100%) of the OSCC cases [82] and CTTN is a candidate driver for this amplification [81]. Overexpression of cortactin promotes cell migration and lymph node metastasis in OSCC [82] and is therefore a promising molecular marker to predict lymph node status. Many binding sites have been reported for cortactin by which important cellular processes involved in metastasis are regulated [82], such as binding to Arp2/3 complex in cytoplasm and cell periphery to regulate nucleation and stabilization of actin [83], binding to F-actin in cytoplasm and nucleus to regulate cell migration [84], binding to ZO-1 in cell tight junctions affects the connection between cell-cell adhesion and actin cytoskeleton [85]. One of the best studied cellular processes involved in metastasis in which cortactin plays a key-role is the regulation of protrusive structures [86]. Invadopodia and lamellipodia are these protrusive structures and enable the invasion and migration of a tumour cell by regulating the actin cytoskeleton and extracellular matrix (Figure 1).