Koos Boeve

16 Chapter 1 In early stage OSCC the SLNB procedure has been reported to be accurate in detecting occult metastasis with a pooled sensitivity of 87% and a pooled negative predictive value (NPV) of 94% in a meta-analysis using 66 studies [30]. Moreover, the SLNB revealed individual lymphatic drainage patterns and detected occult metastasis with a size of just individual metastasis cells [31]. After the introduction in OSCC the SLNB procedure was modified several times [26]. Preoperatively the single photon emission computed tomography (SPECT)-CT scan was added to the SLNB imaging protocol and resulted in detection of additional SLNs in 22% of the patients [32]. Blue dye was part of the SLNB procedure as intra-operatively injected tracer and visualised lymphatic drainage patterns by blue staining [26].This tracer was discontinued in several Dutch centres because blue dye deteriorated the demarcation of surgical resection margins and had only a limited additional value to the preoperative imaging using a radioactive tracer [26]. Step-serial-sectioning with additional keratin staining were added to the pathological assessment protocol to increase the sensitivity of detecting small metastases. Although the high accuracy in detection of occult metastases [30], many of the reported studies consisted of small cohorts and differed in reference treatment for the SLNB negative neck (i.e. END or clinical follow-up), SLNB procedure (e.g. use of a gamma probe, blue dye or SPECT-CT) and pathological work-up (with or without additional keratin staining or step- serial-sectioning). Furthermore, several studies provided incomplete clinico-pathological information. This heterogeneity and lack of complete data underlined the need for studies using complete and homogeneous cohorts. Additionally, the SLNB has some limitations: First, the SLNB procedure seems to be less accurate in patients with a floor of mouth (FOM) tumour what might be caused by the shine-through phenomenon (Figure 4) and resulting in a lower detecting rate of SLNs located in level IA [33]. Secondly, in case of a metastasis positive SLN a complete neck dissection of cervical levels I-V, known as a (modified) radical neck dissection, needs to be done in a second operation. The modified radical neck dissection might be more challenging as a result of fibrosis induced by the SLNB procedure. Finally, although the SLNB is minor surgery compared to the END, it is still an invasive technique for neck staging for early stage OSCC patients of which the majority has no lymph node involvement. Histopathological and (epi)genetic tumour profiling using the biopsy specimen of the primary tumor might be helpful to define patients preoperatively for a more optimal neck strategy with a watchful waiting, SLNB or a neck dissection [34].