For the common skin tumours that spread to the lymph nodes (squamous cell carcinoma and malignant melanoma) prognosis is determined by the size, and in particular, the depth to which the tumour has grown down from the skin surface.  However, once the tumour has spread to the nearest lymph nodes, your prognosis if you have one of these tumours, depends on how many lymph nodes are invaded by tumour and whether the tumour is contained within the lymph nodes, or has broken out of them. 

Lymph node surgery in skin cancer can be both diagnostic (as part of the process of staging a cancer ' quantifying its spread) and therapeutic (attempting to halt its spread and contain it, or palliating its effects in the region to which it has spread).

Sentinel Node Biopsy

To understand why we sometimes perform a procedure called sentinel node biopsy, you need to understand a little of the history of melanoma treatment.

How to treat the regional lymph node basins (the first group of lymph nodes to which an area of skin drains lymphatic fluid, and therefore, the first place to which malignant melanoma or squamous cell carcinoma will spread), has been a contentious topic amongst surgeons for well over a century.  Broadly speaking, one school of thought believes the regional lymph nodes should be removed en bloc at the same time that a tumour had been detected in the skin and removed.  The other advocates waiting to see if the lymph nodes became involved (as judged by enlargement that can be felt on examination) and only removing them at that stage.  This they argue would prevent a proportion of patients undergoing radical surgery unnecessarily.  On the other hand, by the time patients have palpable nodal disease, their tumors have generally already spread systemically, and can no longer be cured by lymph node dissection. 
Certainly evidence from retrospective studies showed patients with thick melanomas had better survival chances if they had their regional lymph nodes removed immediately (i.e. long before any symptoms developed in those nodes that would develop them).

Prospective randomized studies suggest less convincing evidence for electively removing regional nodes, if any, but produce data suggesting benefit in some groups- such as patients with malignant melanomas that are 1-2 mm thick; or who are under 60 years or who have malignant melanomas which have not ulcerated.

Even those who advocate electively clearing regional nodes, agree that those patients whose melanomas have not metastasised derive no benefit and suffer the morbidity and potentially, the complications, of a major surgical procedure.  Ideally therefore, we would like to be able to select the group of patients who are most at risk of having melanoma that has spread to lymph nodes and treat only them by removing their regional nodes.  This goal underpins the sentinel node concept which is based on the  hypothesis that lymphatic spread of cancer proceeds as an orderly process which can be predicted by mapping the lymphatic drainage from a primary tumor to the first or 'sentinel' node in the regional lymphatic basin.  This hypothesis has been borne out in both animal and human studies, and sentinel node biopsy to look for melanoma has been under evaluation as a therapeutic and prognostic tool for many years.  The melanoma team at Guys and St. Thomas' (in which I am one surgeons) is currently the only UK participant in the worldwide study of sentinel node biopsy called the Multicenter Selective lymphadentectomy Trial (MSLT) II.

Current knowledge on sentinel node biopsy (SNB) can be summarized as follows

• There is negligible benefit from performing SNB in patients whose primary melanoma is thinner than 1mm.

• When SNB is performed according to consensus standards, it is predictive of the nodal status of the regional lymph nodes 99% of the time.  In other words, if a sentinel node has no evidence of metastatic melanoma, then there is only a 1% chance that any of the other lymph nodes contains tumour instead. 

• For between 70-80% of patients with metastases in the sentinel nodes, there will be no other involved regional nodes, so whilst the standard of care is considered to be completing the removal of all the remaining nodes in the regional lymph node basis, this will over-treat a significant number of sentinel node positive patients.  On the other hand, for 20-30% of patients with positive sentinel nodes, not proceeding to clear the regional lymph nodes will result in further metastasis of the melanoma from the involved nodes that remain after the sentinel node has been removed and ultimately, the demise of the patient, in part, because of a missed opportunity.

• There is no survival benefit evident from SNB at this stage in the analysis of the data gathered, although the length of disease free interval is improved by SNB and subsequent clearance of the lymph node basin in those patients with positive sentinel nodes.

So, whilst trials continue to evaluate the efficacy and role of sentinel node biopsy, why might you wish to have one if you are diagnosed with melanoma?

First, if you are suitable for a sentinel node biopsy and your biopsy is negative, current data suggest that there is only a 1% chance that you could have melanoma in a different lymph node, which is comforting evidence to suggest no further lymph node surgery is needed.

Secondly, whilst we know that removing a positive sentinel node may in itself be an adequate treatment 70-80% of the time, at least you will have the information you need to decide whether to leave your treatment there or proceed with further, more radical lymph node surgery.

Finally, in the knowledge that removing lymph nodes once they are clinically involved with melanoma is too late in up to 80% of patients because they already have occult distant metastases at that stage, it would seem prudent to embark on a strategy that might prevent such a situation, despite there currently being no clear evidence that sentinel node biopsy provides a survival benefit.


Completion lymphadenectomy & block dissection of regional lymph node basins

Completion lymphadenectomy describes the operation that removes all the remaining lymph nodes in a regional basin where the sentinel node is positive for tumour.
Block dissection of regional lymph nodes describes the operation that removes all the lymph nodes in a regional basin where a lymph node is thought to contain tumour clinically and then proved to contain it after imaging studies and, usually, a needle biopsy and cytology.
Regional lymph node basins are situated in the arm pits, the groins and the neck.  Which is/are involved is simply a function of where on the body the primary tumour was situated.

What does the surgery involve?

Sentinel node biopsy involves a scan followed by an operation.  A weakly radioactive dye is injected into the skin around the scar that remains where the melanoma once was.  The scan picks up the radioactive dye as it passes in the lymph to the sentinel node and this provides me with a two-dimensional picture that localises the lymph node.

Within a few hours of the scan, you will be admitted for surgery and under a general anaesthetic I shall inject a blue dye at the same point which will also flow in the lymph to the sentinel node.
During the operation I will follow the blue trail left within the lymphatics to the sentinel node, helped along the way by using a Geiger counter that picks up a stronger radioactive signal in the sentinel node when compared with the surrounding tissues.

When you wake up you will have a small scar and a drainage tube leading out to a vacuum bottle which prevents the lymph accumulating until the body can re-route the excess that results from disrupting the lymphatics during the operation.  Most people have their drains removed and go home within a day or two.

Completion lymphadenectomy & block dissection of regional lymph node basins are bigger operations.  They take longer for me to do and for you to recover from.  The scar that results is bigger and the wound drains lymphatic fluid for significantly longer as a result of the much larger disruption to lymphatic drainage that results from taking out all the nodes in a particular region.

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