Study: 5-mm Margins Adequate for Small Melanoma in Situ Lesions

skin cancer

New research shed light on the recurrence rates of melanoma in situ (MIS) lesions removed with a 5-mm margin.

"The incidence of MIS has increased significantly over the past decades, and traditional guidelines for treatment of MIS have been excision with a 5-mm clinical margin; however, current Australian and other guidelines now recommend 5- to 10-mm margins," the authors wrote in the study. "This changed recommendation was largely driven by the outcomes of studies using Mohs micrographic surgery, and recent studies using Mohs micrographic surgery are advocating for even wider excisions up to 18 mm for clearance.

The research team looked at a single dermatology clinic and included cases from between 2011 and 2018. The study only included lesions with documented 5-mm margins and more than five years of follow-up. Lesions with margins over 5 mm were excluded, as were those with less than five years of follow-up or requiring multiple excisions. 

The authors reported a total of 351 MIS lesions from 292 patients (average age, 60.3 years; 55.5% female). The most common subtype was superficial spreading melanoma (50.4%), followed by lentigo maligna (30.5%) and lentiginous MIS (19.1%). Lesions were found on the trunk (47.9%), upper limb (27.4%), and lower limb (16.8%); the scalp was the rarest site (0.6%).  78.1% measured less than 10 mm in length and 88.9% less than 10 mm in width. 

According to the results, 99.1% of lesions did not recur clinically after excision with a 5-mm margin. Only three lesions (0.9%) had local recurrences, with no instances of metastatic spread.

"This case series found that excision with a 5-mm margin for MIS of smaller size (<10 mm) on low-risk body sites had a low rate of recurrence," the authors concluded. "Conservative 5-mm excisional margin is likely to be suitable for small MIS on lower-risk body sites."

Source: Sun C, et al. JAMA Dermatology. Doi:10.1001/jamadermatol.2024.1878

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