Koos Boeve

203 English summary ENGLISH SUMMARY Oral squamous cell carcinomas (OSCC) almost always primarily metastasize to the cervical lymph nodes; these are known as regional metastases. Lymph node status is an important prognostic factor for outcome and treatment decision making of head and neck cancer. However, not all regional metastases are clinically detectable with the current diagnostic modalities, such as computed tomography (CT), magnetic resonance imaging (MRI) or Ultrasound guided Fine Needle Aspiration Cytology (USgFNAC). Although they are clinically not detectable, regional metastases occur in 23-37% of the early stage (cT1-2N0) OSCC. These clinically undetectable metastases are known as occult metastases. Occult metastases are conventionally assessed by performing an elective neck dissection (END) after research showed higher rates of overall and disease specific survival compared to a watchful waiting strategy. However, an END has disadvantages: it leads to overtreatment in 63-77% of the cases and has a risk of postoperative morbidity (e.g. shoulder pain, reduced limb movement). Therefore, there is a need for a better and less invasive neck staging modality. In this thesis, we studied the predictive and prognostic value of the sentinel lymph node biopsy procedure, histopathological characteristics and molecular markers for the assessment of neck status in OSCC. Because prior research showed a strong prognostic value for tumour infiltration depth and extranodal extension in OSCC, these histopathological characteristics were incorporated into the 8 th edition of the American Joint Committee on Cancer TNM staging manual. However, the currently available 8 th TNM validation studies lack patients with conservative neck treatment and changes in the classification especially affect patients with small tumours, which are often treated conservatively. In chapter 2 we determined the impact of the implementation of the 8 th TNM staging criteria. In a retrospective cohort of 211 first primary pT1–T2 OSCC patients with surgery as primary treatment, the old and new TNM staging criteria were compared. One hundred and seventy-three patients underwent a neck dissection and 38 patients had frequent clinical neck assessments. Classification according to the 8 th edition criteria resulted in 36% total upstaging with the T classification and 16% total upstaging with the N classification. T3-restaged patients had lower 5-year disease-specific survival rates than T2-staged patients. Postoperative (chemo)radiotherapy could have been considered in another 3% of the patients on the basis of the 8 th edition criteria. We concluded that addition of tumour infiltration depth and extranodal extension in the 8 th TNM classification leads to better staging of oral squamous cell carcinoma and to a selection of patients who might benefit from an adjuvant treatment like postoperative (chemo)radiotherapy.