An introduction Professor Mark McGurk – our founder

Sentinel Node Biopsy

A new development in Oral Cancer - Professor Mark McGurk

"About 40% of patients with mouth cancer present with early disease and are candidates for Sentinel Node Biopsy (SNB). Until now, the risk of neck metastasis was based on statistical evaluation of risk factors (themselves not very reliable).  SNB eliminates this risk.  It can inform the individual patient, irrespective of supposed risk factors, of the exact status of the neck.  It individualises treatment. SNB can safely separate the group of patients with early oral cancer into two distinct groups. The group that has no neck metastasis (75%) can have treatment de-escalated to a simple wide excision of the primary tumour and no neck dissection.  The second group, with early metastatic spread of tumour, represents a high-risk group and can have treatment escalated to include adjuvant radiotherapy or chemo-radiotherapy as required. 

Results show that the survival rate now reported in this group of patients with early cancer is around 93%.  With the publication of the results from the SENT study, NICE has recommended the use of SNB in the UK.

In support of this recommendation, the Head and Neck Cancer Foundation (HNCF), together with Norgine, has set up a national course under the auspices of the Royal College of Surgeons to train Head and Neck cancer centres in the technique of SNB. It is important that the technique be introduced in a coherent and standardised way as it is operator-sensitive and false negative rates as high as 40% have been reported. Only half of these patients can be rescued once the missed metastasis becomes clinically obvious. However, with a careful technique, the false negative rate can be held at about 4-6%.

The technique involves injecting a radioactive tracer around the tumour prior to surgery. This tracer is washed away in the lymphatic fluid to the sentinel node (SN). The tracer then attaches to macrophages in the lymph node and its flow is held up so that a hot spot of radiation accumulates at the site of the SN.  This can be detected by gamma cameras that give the surgeon information as to the area of the neck containing the SN but not information as to its specific position.   During surgery, the sentinel nodes are tracked by means of a hand-held gamma probe and many surgeons will also use blue dye injected around the tumour.  Blue dye can help in the detection of nodes that have already been localised by the gamma signal, but there are disadvantages such as staining at the tumour site, quick transit of the dye through the nodes, and that the colour can be confused with venous structures.

It is for this reason that the wrong node can be harvested. Once the nodes are excised, they are labelled according to gamma counts, presence of blue dye, neck level and size. The nodal bed radiation is recorded after each excision to ensure no hot nodes are left behind and the background radiation is also reported. Any node that is less than 10% of the hottest node is not considered a sentinel node. It is usual to remove 2-3 sentinel nodes but this can be increased in midline cases with bilateral drainage. 

Sentinel nodes are sent for detailed histopathological analysis by serial step sectioning and immunohistochemical analysis. This highly accurate system will detect micrometastasis and isolated tumour cells but it can take several days to complete the protocol. This means that patients who have a positive SNB diagnosed will have the completion neck dissection as a staged procedure, usually within 2-3 weeks of the original surgery. 

What has changed recently is the use of dual tracers – a unique development only being advanced in the UK, which is being vigorously championed by the Head and Neck Cancer Foundation training programme. The tracer molecule can have both radiation and a fluorescent agent attached. The major advantage of the hybrid tracer over blue dye is that the stable compound is retained within the sentinel node by macrophage phagocytosis, resulting in a high level of concordance of fluorescent and gamma signal.  This means that the focus of radiation can direct the surgeon to the area of the neck in question; then, once the tissue plains are opened, the fluorescent image can identify the SN.  It is hoped that the combination of a radioactive and visual tracer will allow the introduction of the SNB technique to the UK with a low error rate of less than 6%. The Head and Neck Cancer Foundation is promoting the use of dual tracers by offering to provide, completely free as a gift for one year, a fluorescent camera to each centre that completes the RCS SNB training course. At present, 15 centres have entered the training programme and seven have completed training and are offering the service to their patients."