Highlights from the Literature Three
Histologic margin status is a predictor of relapse in lentigo maligna melanoma
By Arif Aslam, MBChB, FRACP, FACD
In this article, the authors describe the use of histologic margins as opposed to clinical (surgical) margins to assess risk of relapse in lentigo maligna melanoma (LMM). LMM is the third most common subtype of melanoma after superficial spreading and nodular. While surgery remains the gold standard for treatment, there has been some variation in the suggested surgical margins needed to treat these tumors adequately. For tumors limited to in situ growth, a 5 mm surgical margin is recommended, and a 10 mm margin for those lesions with an invasive component. Studies have demonstrated that the recommended 5mm margin for in situ tumors is inadequate in 8 – 20% of cases. Management of these tumors is challenging because of the potential for subclinical spread, the location in cosmetically sensitive areas, and common occurrence in elderly patients. Because most studies in the literature use surgical margins to guide recommendations, the authors aimed to determine if histologic margin status was a predictor of local recurrence or disease progression.
Cases of LMM treated at Massachusetts General Hospital between 1990 and 2019 were reviewed in retrospective fashion, with 268 cases included for analysis. Demographics as well as tumor features such as anatomic location, Breslow depth, and other standard histologic information were recorded. Treatment modality (wide excision vs staged excision) and outcome information were also recorded. Patients treated with Mohs surgery were not included in this study; however, excisional specimens were processed using complete peripheral margin assessment. Margins were classified as being either negative, positive, or “close” (<3 mm). 59% of patients were male, and 76% of tumors occurred on the head and neck. Median time to recurrence/progression was 3 years with 20.1% of patients having some form of progression. Local recurrence was seen in 13.4% of patients and spread beyond the local site in 6.7% of patients. Histologic margin statuses of positive and close (<3 mm) were the strongest predictors of disease progression/recurrence.
The authors conclude that since histologic margin status was the strongest predictor, positive specimens and specimens with histologic margins <3 mm should consider re-excision given the high rate of disease progression and/or recurrence in LMM patients. It is interesting to note that the cases included in this study were not treated with Mohs surgery and intra-operative immunohistochemical (IHC) markers such as MART-1. Although there are reports of lower rates of recurrence using MMS, these studies report clinical and not histologic margins. It is conceivable that many LMM tumors treated with MMS using IHC have <3 mm surgical margins and a lower rate of recurrence, potentially supporting the use of MMS for these patients. The limitations of this study include the retrospective, single-center design, the exclusion of melanoma in situ, and the lack of clarity on whether the recurrences were melanoma in situ or invasive melanoma.
Progression-free survival is better if margins are negative so re-excision should be considered for patients with a positive or close margin. Long-term follow-up is crucial as progression can occur years after the initial diagnosis.