I recently had the pleasure of spending a morning observing one of my plastic surgical colleagues performing sentinel lymph node biopsy.
What is a sentinel lymph node biopsy?
This is a procedure used in cancer management, for example in breast cancer or in the case of dermatology, in the surgical management of malignant melanoma above a certain thickness in depth of invasion.
The diagnosis of melanoma can be clinical but is confirmed by surgically removing the lesion and having it assessed under a microscope. If a melanoma is confirmed, then it is recommended that a further rim of normal skin be removed around the scar to prevent recurrence of the melanoma at that site. Also if the melanoma cells are active or have spread beyond a certain thickness into the skin, then a sentinel lymph node biopsy (SLNB) is recommended and this has to be performed at the time of the second wider excision.
The sentinel lymph node is the lymph node to which the cancer cells are thought to spread to first.
How do they find this sentinel lymph node?
Before the surgical procedure, the patient undergoes a nuclear medicine scan. This type of scan detects so called ‘hot spots’ of cellular activity. In the case of cancer, these hot spots are thought to reflect cancer cells or spread of cancer cells.
At the procedure, which is performed under general anaesthetic, a radioactive blue dye is injected into the site of the original melanoma. The skin around the original melanoma is removed with nationally agreed margins and then the blue dye is traced using a probe which detects radioactivity to find the sentinel lymph node.
The blue sentinel lymph node is then carefully dissected out and sent off for analysis to see if there are any melanoma cells within it (so called micrometastases).
What happened to those with evidence of micrometastases?
Patients were recommended to have all the lymph nodes removed in that area, called a completion lymph node dissection (CLNB).
And did having a SLNB and a CLNB help prevent the spread of melanoma cells?
Well this is the thing. There has been controversy for some years over this. A trial reported in 2014 showed that there was no significant treatment related difference in melanoma specific survival rate at 10 years from a SLNB. A subsequent study in 2017 showed no benefit in melanoma-specific survival after a CLNB in patients with melanoma and a positive SLNB.
Also, the downsides to the procedure is that there may be overdiagnosis of metastasis to lymph nodes that would never have progressed anyway and there are also the risks of general anaesthesia too.
The upside to the procedure was that it provided some reassurance to those with a negative SLNB, helped those with a negative SLNB avoid a CLNB and also provided some prognostic information for those with intermediate or thick melanomas.
[Morton DL, Thompson JF, Cochran AJ. Final trial report of sentinel-node biopsy versus nodal observation in melanoma. N Engl J Med 2014; 370:599-609.]
[McGregor JM, Saseini P. Sentinel node biopsy in cutaneous melanoma; time for consensus to better inform patient choice. Br J Dermatol 2015; 172:552-554.]
[Faries, MB, Thompson JF, Cochran AJ et al. Completion dissection or observation for sentinel-node metastasis in melanoma. N Engl J Med 2017; 376:2211-2222.]
So why are we still doing SLNB?
Well, after the 2017 trial, CLNB fell out of favour.
However, novel adjuvant therapies have evolved for the treatment of micrometastatic melanoma, patients with clinically detectable lymph node spread and patients with spread of melanoma to the skin around the previous primary melanoma (so called in-transit metastases).
Trials with adjuvant treatments have shown clear improvement in disease-free survival with some suggestions of cure.
[McKean MA, Amaria RN. Multidisciplinary treatment strategies in high-risk resectable melanoma: Role of adjuvant and neoadjuvant therapy. Cancer Treatment Reviews 2018;70:144-153.]
[Eggermont AMM, Robert C & Ribas A. The new era of adjuvant therapies for melanoma. Nat Rev Clin Oncol 2018; 15(9):535-536.]
How is one adjuvant treatment chosen over another?
Well basically, the findings at SLNB helps stratify patients into low-, intermediate- and high-risk and this basis is what helps in the selection of which adjuvant therapy should be used.
[Ascierto PA, Borgognoni L, Botti G et al. New paradigm for stage III melanoma: from surgery to adjuvant treatment. J Transl Med 2019;17:266.]
[Verver D, van Klaveren D, van Akkooi ACJ et al. Risk stratification of sentinel node-positive melanoma patients defines surgical management and adjuvant therapy treatment considerations. Eur J Cancer 2018;96:25-33.]
It is interesting therefore to read a Letter to the Editor in the August edition of the British Journal of Dermatology about how the role of the sentinel lymph node biopsy has now changed. In the author’s words, it is now a ‘game changer’ in that those with a negative SLNB remain under clinical follow up whereas those with a positive SLNB are offered adjuvant therapy.
[McGregor JM. The sentinel node biopsy has come of age. Br J Dermatol 2019;181:423-427.]
Dr Sandy Flann, Consultant Dermatologist.