Koos Boeve

73 SLNB in oral cancer after previous neck treatment INTRODUCTION Presence of lymphatic metastases in the neck is consistently observed as main prognostic factor in patients with oral squamous cell carcinoma (OSCC) [1-3]. Sentinel lymph node biopsy (SLNB) proved to be reliable as diagnostic staging modality for detection of occult lymph node metastases: in a large recent meta-analysis a pooled sensitivity of 87% (95% CI 85-89%), a negative predictive value of 94% (95% CI 93-95%) and an AUC of 0.98 (95% CI 0.97-0.99%) were found [4]. These meta-analysis results are based on patients with primary OSCC and a previously untreated neck. Despite the relatively common local recurrences and second primary tumours in head and neck cancer, only one study of Flach et al. reported about the accuracy of the SLNB in 22 patients with a previously treated neck [5]. It is well known that patients with OSCC suffer a high risk for local recurrences (10-30%) and an annual risk of 3-4% for developing second primary tumours [3,6-8]. Previous treatment of the neck most likely alters lymphatic drainage patterns. Current evidence about the drainage patterns in previously treated OSCC patients using SLNB is limited to a study by Flach et al. (n = 22) and a feasibility study by Pitman et al. (n = 5) [5,9]. Experience of alteration in lymphatic drainage patterns after previous treatment has also been reported in breast cancer and melanoma [10-15]. While gaining more and more experience with SLNB in our institutions during the last years, SLNB has been used increasingly as staging method in patients with a previously treated neck. Moreover, SLNB is valuable in assessment of the individual lymphatic drainage patterns, compensating for potential variabilities as a result of previous treatment which were reported in 67% of the cases by Flach et al [5]. However, since the study of SLNB in OSCC patients with a previously treated neck consisted of only 22 patients, more research had to be performed to confirm the findings of that study [5]. The aim of this study was to assess the accuracy of SLNB and secondly, to evaluate the lymphatic drainage patterns in a consecutive cohort of cT1-2N0 patients with a previously treated neck in three Dutch head and neck cancer centers. METHODS In three Dutch head and neck centers 53 patients diagnosed between 2007 and 2016 met the inclusion criteria and were retrospectively analyzed. Patients with early stage local recurrent disease or second (or even third) primary squamous cell carcinoma of the oral cavity or oropharynx with a clinically negative neck and surgical resection of the tumour combined with SLNB staging of the neck were included (cT1-2N0, following the 7 th TNM staging classification, Table 1). In their history, all patients had received prior treatment