Koos Boeve

183 General discussion and future perspectives patterns with the SLNB procedure as reported in chapter 5 ) , the SLNB might also be a suitable neck staging technique in cN0 maxillary OSCC and might prevent these patients for undertreatment of retropharyngeal and contralateral located lymph nodes. Limitations of the SLNB procedure in oral squamous cell carcinoma Although the high accuracy in detecting occult metastasis and the assessment of individual lymphatic drainage patterns, the SLNB also has several limitations and uncertainties such as: lower accuracy in floor of mouth tumours, a second surgery in SLNB positive patients and the strategy after a positive SLN with isolated tumour cells. Higher false negative (regional recurrences) rates up to 25% have been reported for the SLNB procedure in floor of mouth (FOM) tumours [16,62] compared to the 6% in the other OSCCs [1]. This lower accuracy is caused by the shine-through phenomenon [11,63]: the hotspot of the SLN is located within the hotspot of the tumour on lymphoscintigraphy and SPECT-CT. As described also in chapter 3 , a level I dissection was proposed in a study in which 50% of the SLNs in level I of FOM tumours were detected only intra-operatively using the level I dissection and not preoperatively by lymphoscintigraphy or SPECT-CT [63]. Another option is the combination of a conventional radio-guided tracer with a fluorescence tracer indocyanine green (ICG)-(99m)Tc-nanocolloid [64]. Seventy-five percent of the SLNs in five patients with a FOM tumour were solely detected by this hybrid tracer. The surgical consensus guidelines implemented these options for cases with a high potential of shine- through in level I and recommend a low threshold to explore level I [16]. The clinical value of isolated tumour cells (ITCs) and micrometases, defined as a size of < 0.2 mm and 0.2-2 mm [65,66], respectively, in SLNs of OSCC patients is not completely clear. Before a neoplastic cell has disseminated from the primary tumour site and formed a metastasis in a lymph node (or other organ), these tumour cells have to go through different processes (e.g. detachment, invasion, migration, extravasation, cell division, etc.) [67,68]. If one of these processes is not completely fulfilled, these disseminated tumour cells will most likely not result in a metastasis [67]. For example, a cell can reach a lymph node or other organ, but stay there in a dormant state (disseminated tumour cell (DTC) [67,69,70]. Probably, these DTCs are a result of mechanical manipulation during biopsy [67,71] and lack ability to grow into an invading metastasis [67]. ITCs and the micrometastases detected in lymph nodes by the SLNB procedure might be such dormant DTCs [70] and harvesting of these SLNs might be therapeutic and consequently, these patients might not benefit from an additional MRND. In breast cancer, a recurrence rate of 0.4% was reported in cases with micrometastases in their SLNs (ITC information was not available) with five years of follow-up and without a benefit for patients additionally treated with axillary lymph node dissection [72]. This observation resulted for breast cancer in a pN0(i+) classification for SLNs