**8. Future directions**

It is widely accepted that macrometastases and micrometastases should undergo a completion neck dissection, however management of ITC remains uncertain without a clear consensus. This is a significant issue as the incidence of ITC ranges between 14 and 27% of positive SLNs [27, 30, 36] and the two RCTs managed this subgroup with differing strategies. The Senti-MERORL trial treated ITC with observation, and in those 11 patients there were no nodal recurrences [15]. Conversely

the Japanese RCT treated ITC with a completion neck dissection [34], however subgroup outcome data was not published. A retrospective Dutch study analysing outcomes for patients undergoing SLNB for OCSCC found a SLN positivity rate of 22% (107/488 patients) and of these patients, 15 (14%) had ITC, 31 (29%) had micrometastases and 61 (57%) had micrometastases. 13 of the patients with ITC underwent a neck dissection with 1 patient having additional positive lymph nodes, and the other 2 patients had adjuvant radiotherapy, and did not develop regional recurrence during follow up [36]. While ITC is considered to represent node negative disease in the setting of breast cancer [9], management of these patients remain uncertain in the setting of OCSCC and further data is required to clarify both the natural history and management outcomes for this subset of patients.

Intraoperative lymphoscintigraphy is a developing technique which has particular utility in the management of oropharyngeal or laryngeal SCC with a SLNB. These tumours are unable to be injected with a radiotracer in an awake patient for a preoperative assessment [37]. Indocyanine green (ICG) is readily taken up by lymphatics and can be identified intraoperatively using a near-infrared fluorescence camera to locate the sentinel lymph node [38]. The use of ICG does not cause any staining of the primary site as seen with use of patent blue dye, and also provides an immediate result, which offers obvious benefits in the setting of intraoperative sentinel lymph node identification. However, it does not provide the detailed drainage information with anatomical referencing that is provided by performing radiotracer based lymphoscintigraphy with a SPECT/CT. While techniques such as skin compression have been described to identify lymphatic drainage and the SLN before making a skin incision [37], often the skin flaps need to be raised to comprehensively assess the nodal basins [39]. In addition, the ICG signal spreads rapidly with time and thus second tier lymph nodes can be hard to distinguish from the true sentinel lymph node [40]. The use of hybrid tracers which assemble ICG with a radiocolloid to increase the retention time in the sentinel lymph node has been described [38], and may have an increasing future role, along with the use of intraoperative SPECT scanners, to counteract the disadvantages of using ICG alone. However, this is an exciting new tool which can be utilised to expand the utility of the SLN technique.
