What are the recommended safety margins for radical excision of a primary melanoma (in situ)?
As for invasive melanoma, the treatment for melanoma in situ, including lentigo maligna (LM), is complete surgical excision with clear margins. For excision to be successful, a margin of clinically normal skin must be included because macroscopically invisible tumour often exists at the margins. Use of magnification, bright light and possibly Wood's lighting or confocal microscopy for preoperative marking are useful methods for improving the accurate definition of detectable margins.
There are no RCTs and limited case series data to help direct excision of melanoma in situ. Given this lack of evidence, in 1992 consensus guidelines were published suggesting that 5 mm excision margins should be adequate for melanoma in situ. However, recent studies have shown that 5 mm margins might be inadequate in some situations and can lead to significant rates of disease recurrence, particularly for head and neck disease.
In many cases, in-situ melanoma margins can be accurately determined pre-operatively by careful examination and an adequate margin of ≥ 5mm can be confirmed by pathology. In some cases Mohs surgery or staged serial excision may have a role, but the accuracy is lesion dependant and operator dependant. Unfortunately Mohs surgery currently is not universally available or affordable in Australia. Most international guidelines suggest 5 mm margins for melanoma in situ. The BMJ Best Practice monograph on melanoma states that “For melanoma in situ the recommended surgical margin is 0.5 cm. Some studies have found that this margin will be inadequate in some (up to 50% of) cases of melanoma in situ and particularly lentigo maligna. Options for dealing with this include: (a) wide excision with 1-cm margin; (b) staged excision with careful margin assessment; and (c) Mohs surgery.” The 2010 UK guidelines state 5 mm margins to achieve complete histological clearance. The 2011 US guidelines go further recommending 5 mm-1 cm margins and state that "wider margins may be necessary for lentigo maligna subtypes".
Evidence summary and recommendations
|There is case series evidence suggesting that 5 mm margins are often adequate to treat melanoma in situ. However, in some cases of melanoma in situ 5mm margins are inadequate and may lead to significant rates of disease recurrence.||IV||, , , , , |
Excisions should have vertical edges to ensure consistent margins.
For all melanomas, minimum clearances from all margins should be stated/assessed. When necessary, further excision should be performed in order to achieve the appropriate margin of clearance.
Where tissue flexibility is limited, a flap repair or skin graft may be necessary subsequent to an adequate margin of removal.
Most primary melanomas can be treated as an outpatient under local anaesthesia or as a day-case.
Patients should be informed that surgical excision may be followed by wound infection, bleeding, haematoma, failure of the skin graft or flap, risk of numbness, a non-cosmetic scar, dehiscence and the possibility of further surgery.
Supplement. Moh's surgery and staged serial excision
A large prospective study assessed complete clearance of 1120 melanomas in situ excised by Mohs micrographic surgery with frozen-section examination of the margin. Six millimetre margins were adequate for complete clearance in 86% of all tumours; 9 mm margins were adequate for complete clearance in 98.9% of all tumours. A 1.2 cm margin yielded 99.4% clearance, 1.5 cm margin yielded 99.6% clearance, and 3 cm margin yielded 100% clearance. The authors state that “the frequently recommended 5 mm margin for melanoma is inadequate. Standard surgical excision of melanoma in situ should include 9 mm of normal-appearing skin, similar to that recommended for early invasive melanoma”. This study includes a mixture of cases of melanoma in situ, both LM and non-lentigo maligna type, and it is possible that LM requires a wider margin than other melanomas in situ.
A retrospective review of 192 cases of melanoma in situ found that LM required wider margins for complete excision than did non-lentigo maligna melanoma in situ.
In another retrospective study of 117 LM and lentigo maligna melanoma (LMM) cases treated with a staged margin-controlled excision technique, the mean total surgical margin required for excision of LM was 7.1 mm and was 10.3 mm for LMM. Of the tumours diagnosed as LM on initial biopsy specimen, 16% were found to have unsuspected invasion. Total surgical margin was associated with initial clinical lesion diameter. The authors concluded that the standard excision margins for LM and LMM are often inadequate and occult invasive melanoma occurs in LM. Dermatoscopy and confocal microscopy may be useful in defining margins before excision of melanoma in situ.
A retrospective review of 343 cases of melanoma in situ on the head and neck treated by Mohs micrographic surgery showed that 65% of cases were cleared by a 5 mm margin whilst 15 mm margins were needed to obtain a 97% clearance rate. The authors concluded that “melanoma in situ on the head and neck can spread significantly beyond the clinical margins and demonstrates the importance of confirming clearance histologically before closure procedures. Mohs surgery has the advantage of total margin evaluation and where available it may be reasonable to start with 5 mm margins. Where Mohs surgery is not a treatment option, the authors would advocate larger excision margins of ≥ 10 mm.”
In a study of 51 cases of facial LM and thin (<1 mm) LMM, with LMM present in nine lesions (average Breslow depth, 0.65 mm), peripheral margin control was performed with repeated margin excision until histological clearance of the lesion. Margins required for clearance of LM and LMM averaged 1.0 and 1.3 cm, respectively. No recurrences were identified with long-term follow-up. Immediate reconstruction was performed in all cases.
In another retrospective review of 293 cases of LM and LMM treated by geometric staged excision, the mean margin to clearance after excision was 6.6 mm for LM and 8.2 mm for LMM. Of concern, 26.6% of LM would not have been adequately excised using traditional 5 mm margins. The rate of recurrence of after geometric staged excision was 1.7% with a mean of 32.3 months of follow up. A total of 11.7% of LMM was initially diagnosed as LM on biopsy, with the invasive component discovered only after excision.
Zitelli comments that “Many surgeons shudder at the thought of such wide margins on the head and neck, and therefore it is important to note that Mohs surgery using MART 1 immunostains offers a way to keep more narrow margins for the majority of patients yet still have the ability to identify the outlier patients with wide subclinical extensions of MIS. The importance of clearing MIS on the first procedure is that recurrence appears as invasive melanoma of 1-mm thickness in 23% of recurrences.”
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