Koos Boeve

18 Chapter 1 Histopathological and molecular tumour biomarkers predicting lymph node status in OSCC Tissue from tumour biopsy or surgical resection material enables to associate tumour characteristics with lymph node status in OSCC. Histopathological tumour characteristics such as tumour infiltration depth, pT status, perineural invasion, lymphovascular invasion, degree of differentiation and pattern of invasion have been associated with lymph node status for decades [35-39]. Of these histopathological characteristics, tumour infiltration depth was reported as an independent predictive marker with the highest predictive value and has been used in clinical practice for risk assessment of lymph node status [21,22,35]. Although some of the other histopathological tumour characteristics (lymphovascular or perineural invasion, close surgical resection margins or a pT3-T4 staged tumour) are used as adverse features to select patients for adjuvant radiotherapy, these characteristics are not used as risk assessment to select patients for a neck dissection. Lack of clear validations and large intra- and interobserver variability might be reasons why these markers are not introduced in the clinical setting for predicting lymph node status [40]. For example, tumour pattern of invasion was associated with lymph node status [41]. However, an analysis of five different scoring methods for tumour invasion pattern showed just a moderate reproducibility [40]. More recently, molecular tumour biomarkers have been studied widely for their association with lymph node status. Many different cellular processes are involved in metastasis of tumour cells, such as cell adhesion (detachment of the primary tumour), cell mobility (movement to vascular structures), cell remodelling (passing vascular walls), resistance to blood flow (adhesion to vasculature), direct exposure to immune system, homing and cell division (metastasis formation in the lymph node) [42-44]. Some of these cellular processes are (de-)regulated by increased expression of proto-oncogenes and the inactivation of tumour suppressor genes caused by (epi)genetic alterations [45,46]. For example, amplification of the 11q13 chromosome is such a genetic alteration and one of the most frequently (36%) detected alterations in head and neck cancer [47]. CTTN , CCND1 and FADD are three genes located in the commonly amplified region at chromosome 11q13 and overexpression of their proteins is associated with shorter survival and positive lymph node status in head and neck cancer [48-50]. CTTN encodes for cortactin, a protein with multiple binding domains such as F-actin, Src and Erk [51]. Cortactin is involved in cytoskeleton formation, cell morphology and cell migration which are important processes to enable a cell to metastasize [51]. Expression of cortactin results in migration in vitro [52] in agreement with the observed association with lymph node status in patient biopsies of the 11q13 amplification [53]. The CCND1 gene encodes for the cyclin D1 protein, which is especially known for promoting cell cycle progression during G1 [54], but also plays a