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Sentinel Lymph Node Biopsy

Sentinel Lymph Node Biopsy (SNB) ​is an established technique used in the treatment and staging of Melanoma. We know that Melanoma has the ability to spread via a haematogenous (blood) or lymphatic route. 

Sentinel Lymph Node Biopsy

It can take some time before spread is noticed either by the patient or clinician (usually in the form of a lump) or identified on a scan. Scans will only identify a lump once it gets to a certain size. A SNB attempts to identify whether spread has already occurred on a microscopic level. If this spread is identified it can in some cases be treated early. 

The Sentinel node is the hypothetical first lymph node in a chain of lymph nodes. The technique of identifying the sentinel node in Melanoma is in two stages. The first stage involves injecting of the Melanoma scar with a radioactive substance called Technetium-99 in the Nuclear medicine department. The radiographers then trace the substance as it accumulates in the lymph node or lymph nodes that drain that skin. This can be done on the day before or day of surgery. In some cases multiple drainage sites are identified which may either involve taking multiple lymph nodes or deciding that inaccuracies in assessment are likely to occur. In the latter case it may mean not continuing with the second stage. 

Sentinel Lymph Node Biopsy

The second stage takes place in the operating theatre. In most cases this is under a General anaesthetic (asleep). The melanoma scar is injected with a blue dye at the same site as the previous T-99 injection. The information provided by the proceeding scan and a sentinel node probe in theatre allows the surgeon to find the lymph node. The blue dye enables better visualisation of the node itself. The surgery therefore involves a wide excision of the Melanoma scar and an incision over the identified lymph node. 

Risks of surgery specific to SNB include seroma, lymphoedema (rare) and 'false' histology. Essentially a negative SNB (no evidence of disease) does not mean that the Melanoma can not spread but it does put the patient in a lower risk group.

Standard five year surveillance is given to all patients regardless of SNB results.

Sentinel Lymph Node Biopsy

A positive SNB (evidence of Melanoma in the Sentinel node) will often result in a referral to the Oncologists for consideration of further treatment.

If SNB is considered not appropriate, or the patient choses not to have a SNB this does not necessarily preclude further treatment.


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