Koos Boeve

79 SLNB in oral cancer after previous neck treatment procedure appears technically more challenging compared to initial surgery. In a cohort of 27 patients, SLNs were found in two groins at unpredicted localizations and four lateral tumours showed bilateral SLNs [19]. Beasley et al. reported about the feasibility of SLNB in recurrent melanoma (107 patients) and also found in 24% of the patients additional sites of SLNs compared to the first SLNB procedure [15]. Although it is difficult to compare different tumour types, a trend towards a lower identification rate of SLNs compared to untreated patients was observed in present and all above mentioned studies. The most common explanation is the damage of lymphatic pathways due to prior treatment and a more difficult technical procedure to harvest SLNs in previously treated nodal basins. In untreated OSCC identification rates of 97-98% have been reported, while in this study a rate of 85% was found [16,17,20,21]. All patients without harvested SLNs had radiotherapy in history, sometimes combined with surgery. This lower identification rate was not observed in patients with a prior SLNB procedure, possibly reflecting that SLNB ensures less damage to lymphatic vessels compared to radiotherapy. Furthermore, despite the lower identification rate in previously treated patients no lower NPV of the SLNB for neck staging was found in this study. This might indicate that lymphatic drainage patterns in these patients are not only aberrant, but may even be absent. Nonetheless, this study included only three patients with positive SLNs and one patient with a regional recurrence after a negative SLNB procedure. Due to the low number of SLN positive patients and regional recurrences, it might be prematurely to conclude that SLNB is a reliable procedure in previously treated patients. This is also reflected in a sensitivity rate with a wide 95% CI. However, the high NPV of 98% with a 95% CI of 88-100% strongly suggest that SLNB is a promising procedure for these pretreated patients, but its reliability needs further investigation. Although surgery of the lymphatic drainage patterns is part of the SLNB procedure, the procedure is strictly not part of the treatment but belongs to the diagnostic modalities for neck staging. Therefore subanalysis of patients with a history of neck treatment (neck dissection and/or radiotherapy) are presented in the results regarding the accuracy of the SLNB procedure and lymphatic drainage patterns. These figures indicate that in OSCC patients who had undergone more extensive treatment of the neck (i.e. neck dissection and/or radiotherapy) lymphatic drainage follow more frequently an unexpected pattern or was absent (35% vs 30%). Due to the low number of lymph node metastases (2 and 3) the sensitivity of SLNB (50% and 75%) could not sensibly be compared. Unexpected drainage pathways are generally reported in all tumour types, including our study. These findings strengthen the value of SLNB in assessing the individual lymphatic drainage pattern. In patients who received already prior treatment (e.g. radiotherapy) it