Koos Boeve

55 SLNB in early oral cancer INTRODUCTION Regional metastases occur in 23-37% of the early stage (cT1-2N0) oral squamous cell carcinomas (OSCC) [1-3]. Lymph node status is an important prognostic factor for outcome and treatment decision making of head and neck cancer [1-8]. However, not all metastases are clinically detectable with the current diagnostic modalities [9-11]. Occult metastases are conventionally treated by removal of the lymph nodes by elective neck dissection (END) after research showed higher rates of overall and disease specific survival compared to a watchful waiting strategy [12]. However, an ENDhas 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) [13]. Therefore, there is a need for a better neck staging modality. The sentinel lymph node biopsy (SLNB) was introduced in oral cavity cancer as a less invasive lymph node staging technique after successful implementation in melanoma and breast cancer [5]. The limited number of lymph nodes (LN) with the SLNB enables a more meticulous pathological examination incorporating step serial sectioning (SSS) and additional immunohistochemistry (IHC) [14]. Recently, Liu and Wang reported a meta- analysis of 3566 early stage OSCC patients from 66 studies with a pooled sensitivity of 87% and negative predictive value (NPV) of 94% for SLNB in detecting occult metastasis [15]. However, many of these studies consist of small cohorts and differ in reference treatment, SLNB localisation technique (e.g. use of gamma-probe, blue dye or single photon emission CT (SPECT-CT)) and pathological work-up (with or without IHC or SSS). Furthermore, several studies provide incomplete clinico-pathological information. This heterogeneity and lack of complete data underline the need for more studies using complete and homogeneous cohorts. The aim of this study was to determine the sensitivity and NPV of the SLNB in detecting occult metastases in a large, well-defined cohort. For this purpose, we used a retrospective cT1-2N0 OSCC cohort of 91 patients all treated by primary surgical resection, neck staging with the SLNB procedure and routine follow-up as reference standard for the SLNB negative neck. PATIENTS AND METHODS Ethical consideration Sentinel lymph node biopsy was part of standard treatment and data were retrospectively gathered from existing data sources; therefore no approval from the hospital research ethics board was required according to the Dutch ethical regulations [16,17]. Five patients were