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Successful Treatment of Lentigo Maligna and Lentigo Maligna Melanoma with Mohs Micrographic Surgery

Lentigo maligna (LM) and lentigo maligna melanoma (LMM) can be among the most difficult skin cancers to treat. This is because the clinical margins are difficult to see and the tumors can be large. In two recent articles the authors review their experience using Mohs micrographic surgery (MMS) for the treatment of LM and LMM.

In one study, 45 patients with LM (26) or LMM (19) were treated with MMS. MMS frozen sections followed by rush permanent sections were used to excise the clusters of atypical melanocytes. The MMS frozen sections allowed for more rapid removal of the tumors than when permanent sections are used alone. The permanent sections provided confirmation of the atypical melanocytes detected on frozen sections. All 45 patients were free of disease at an average of 29.2 months after treatment.

The other study evaluated MMS and adjunctive staining for HMB-45 and antibodies to S-100 protein in 16 patients with LM. The interpretation of the MMS frozen sections did not differ from the interpretation of the permanent sections in any samples. Fifteen of the 16 cases of LM showed diffuse staining with the HMB-45 antibody. Staining with the S-100 protein was focal and non-specific compared to staining with HMB-45. The S-100 protein stained nevi, melanocytes in lentigines, and normal melanocytes in sun-exposed skin, while HMB-45 did not stain any of these benign entities. One of the 16 patients had a recurrence 8 years after surgery. (Patients were observed for 5 to 9 years.)

Comment: The reason the cure rate for LM and LMM is higher with MMS than with conventional surgical excision is that 100% of the surgical margin is examined with MMS, as compared with less than 0.1% when the standard "bread loaf" method of pathologic preparation is used with conventional surgical excision. MMS also removes less normal tissue. However, interpreting melanocytic lesions on frozen sections is not without difficulty. The artifact rendered by freezing such specimens can make it more difficult to make a definitive diagnosis as compared with evaluating surgical margins. The vacuolization that occurs with freezing skin can resemble melanocytes.

HMB-45 immunostaining has been used to help confirm the presence of atypical melanocytes on the MMS frozen sections. HMB-45 shows high specificity and sensitivity for atypical melanocytes. It should be noted, however, that HMB-45 staining is not specific for malignant melanocytes and has been previously reported within melanocytes at the edges of lentigo maligna. Use of HMB-45 staining would therefore increase the likelihood of false positive readings. Immunoperoxidase staining is also a reasonably expensive procedure and may not be available with rapid turnaround times in most hospitals. Although the authors of these reports recommend MMS for the treatment of LM and LMM because it limits the risk of local recurrence and gives a cure rate superior to that reported with conventional surgical excision, a high level of expertise is necessary to avoid serious errors in the diagnosis of melanocytic lesions on frozen section.

— RL Moy and BR Smoller

Published in Journal Watch Dermatology September 1, 1994

Citation(s):

Cohen LM et al. Successful treatment of lentigo maligna and lentigo maligna melanoma with Moh's micrographic surgery aided by rush permanent sections. Cancer 1994 73 2964-2970.

• Medline abstract (Free)

Robinson JK. Margin control for lentigo maligna. J Am Acad Dermatol 1994 31 79-85.

• Medline abstract (Free)

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