Koos Boeve

181 General discussion and future perspectives accuracy in detecting occult metastasis in primary early stage OSCC ( chapter 3 ) using the SLNB procedure could be used as reference for other centres. The protocol reported in chapter 3 is a minor surgery alternative for neck staging with the conventional END regarding complications, postoperative morbidity and cost-effectiveness. Individual lymphatic drainage pattern assessment in head and neck cancer using the SLNB procedure Another advantage of the SLNB procedure is the assessment of individual lymphatic drainage patterns. Normally in lateralized OSCC tumours, lymphatic drainage goes to lymph nodes located in the ipsilateral levels I-III [38]. An analysis of 583 OSCC patients with T1-T4 staged tumours, revealed no skip metastasis to level IV or V, or in other words, metastases in level IV or V were always accompanied by at least one metastasis in level I-III [39]. In chapter 3 [11], we did not find skip metastases at the ipsilateral side, however we reported bilateral drainage patterns in 37% of the early stage OSCC cases while also cases with well lateralized tongue tumours were part of this cohort. Moreover, one patient with a well lateralized tongue tumour only had a SLN (negative for metastasis) at the contralateral side of the neck compared to the tumour [11]. Contralateral drainage of lateralized tumours is not uncommon and reported in 10% of the OSCC cases [16,24]. After an END, up to 39% of the regional recurrences are reported in the contralateral neck [40]. The assessment of individual drainage patterns with the detection and harvesting of SLNs with unexpected drainage patterns using the SLNB procedure, might prevent patients for undertreatment. Therefore, if surgical removable, the consensus guidelines recommend harvesting of SLNs located in unexpected locations (i.e. not in ipsilateral levels I-III), because these SLNs might represent an anatomical variation with a direct lymphatic drainage pattern and are therefore potential locations for the first metastasis deposits [16]. The assessment of individual drainage patterns using the SLNB procedure was also helpful in exploring the drainage patterns of patientswith a previously treatedneck ( chapter 4 ) [41,42]. Local or local-regional recurrences are reported in 10-30% of head and neck squamous cell carcinomas (HNSCC) [43]. At the time of diagnosis of a local recurrence or second primary OSCC, many of these patients already underwent a SLNB procedure, neck dissection or radiotherapy for their first primary tumour. Knowledge about how these treatment altered lymphatic drainage patterns was restricted to two studies with a total of 27 patients [44,45]. Therefore, no consensus for the neck strategy of these patients was available in literature. In chapter 4 [42], we reported on the accuracy of the SLNB in 53 early stage (cT1-2N0) OSCC patients with earlier treatment (dissection or radiotherapy) or surgery (SLNB) of the neck and analysed the lymphatic drainage patterns of these patients. With the low number of events (lymph node metastases 3/45 and regional recurrences 1/45 ) taken into account, the SLNB procedure seemed accurate in detecting occult metastasis. No drainage patterns