Sentinel Node Biopsy
For people with a stage 2 melanoma, it is important to examine and stage lymph nodes. What cancer staging means, is, determining how much cancer is present in the body, and to what areas it has spread. In melanoma, the depth of invasion of the primary tumour (the Breslow thickness) is related to the risk of spread of melanoma to the local lymph nodes.
When a primary melanoma has a Breslow thickness of >1mm (or sometimes 0.8mm with some adverse other features) there is a small risk of lymph node spread, which increases proportionally with the tumour thickness. Therefore it is important to assess the local lymph nodes for melanoma involvement.
There are three ways used to assess the local nodes: clinical examination, ultrasound and sentinel node biopsy.
Ultrasound is a good way to identify abnormal nodes and can identify an area of melanoma from about 4-5mm large, and some centres offer serial ultrasounds to monitor the lymph nodes.
Sentinel node biopsy is a procedure that takes place at the same time as a wide local excision for melanoma. Usually, a blue dye is injected into the scar from the original melanoma excision, as is technetium, a radioactive isotope. Both the dye and the isotope will drain to the first lymph node the lymphatic channels from the area ok skin harbouring the melanoma. If melanoma is going to spread via the lymph nodes it usually will go to this first or ‘sentinel’ node in the first instance.
Lymph nodes are small globes of tissue that harbour immune cells, hence the analogy to a sentinel – they are like barracks for the different types of immune cells that fight cancer and infection. The radioisotope allows us to identify the node (or nodes) before operating, and we can map (identify) the particular node on 2 types of scans (SPECT – a type of CT, and lymphoscintigraphy). Using a gamma-probe to pick up the radioactive signal and identifying the blue dye allows us to identify the sentinel node after making a very small incision over the node (this may also be marked by an ultrasound).
The procedure is straightforward, but does have complications – allergy to the blue dye, sometimes the sentinel node cannot be identified, one can get infections or seroma in the wound, and a small percentage of people may develop lymphoedema or numbness in the region of surgery.
One to three nodes are usually examined, to a fine level of details, which can take up to 2 weeks to process fully. If the node is positive, then the melanoma is staged as Stage IIIA or B depending on tumour thickness. This may have relevance for being eligible for clinical trials of adjuvant treatment which aim to reduce the risk of melanoma recurrence after clearing disease with surgery, and in the near future, eligibility for adjuvant treatment regimens, as they are more clearly defined.
Recent updates on Sentinel Node Biopsy
Until recently, if the sentinel was positive for melanoma, most centres would recommend a dissection (surgical removal) of all of the lymph nodes in the region – usually the axilla (armpit) or the groin. The rationale of this approach was to clear out any other nodes that may have the disease (‘non-sentinel nodes’) which could progress in future (around 10-15% of other nodes may have melanoma present) to gain control of the melanoma, and also because finding other nodes would give useful prognostic information – indicating a higher risk of spread elsewhere.
A major international randomised trial, MSLT-1 (Multicenter Selective Lymphadenectomy Trial) was set up to test whether performing a sentinel node biopsy and removing all of the nodes early if a positive node was identified would improve survival, when compared to clinical examination and taking out the nodes if they became clinically apparent (usually swollen).
Although people have argued that removing all nodes when the sentinel node is positive, the trial did not show improved survival in these patients (http://www.nejm.org/doi/full/10.1056/NEJMoa1310460). That was a very important finding, as a lymph node dissection can have significant morbidity (surgical side-effects) – up to 15% of people may develop lymphoedema, and in the groin 30-40 of people develop wound complications such as infection, wound breakdown and seromas.
Two recent trials, the follow up MSLT trial (MSLT-2) and the German DeCOG-SLT have further informed our approach to sentinel node biopsy. Both were randomised trials that examined whether there was a difference in survival when monitoring patients with ultrasound after a positive sentinel node biopsy, in comparison with dissecting all of the lymph nodes.
Both trials found that there was no difference in survival, but the majority of patients could avoid a further operation and complications. If lymph nodes were identified during follow up, they could be safely removed. The number of patients in MSLT-2 who had a recurrence of melanoma in the lymph nodes only was 6.4% higher in the ultrasound group. Although one can consider a node dissection, in particular, if there is no facility for ultrasound surveillance at your treating centre, or if it is a personal preference, in general, it need not be performed, which is good news for many melanoma patients.