DS19 Wide local excision for melanoma in situ of the trunk and limbs: when is enough enough?

Abstract

Melanoma in situ (MIS) is defined by malignant melanocytes confined to the epidermis. Current NICE guidance recommends a 5-mm excision margin; however, this is based largely on expert opinion rather than randomized trial evidence. Much of the existing literature focuses on lentigo maligna, which differs biologically from superficial spreading MIS on the trunk and limbs. This has led to debate regarding the necessity of routine wide local excision (WLE) following narrow-margin excision in nonchronically sun-exposed sites. This study was designed to determine the frequency and characteristics of residual disease following histologically complete excision of MIS on the trunk and limbs in a UK tertiary centre. We conducted a retrospective review of 295 cases of MIS of the trunk and limbs excised between 2015 and 2019. Lesions of the head, neck and acral sites, and those with lentiginous morphology were excluded. Histological margins, presence of regression and WLE outcomes were recorded. Residual disease was defined as MIS identified in the WLE specimen following a primary excision with reported clear peripheral margins. The cohort comprised 294 patients (mean age 62.7 years); the mean peripheral histological margin was 1.6 mm. WLE was performed in 268 of 295 cases (90.8%). Residual disease was identified in 8 WLE specimens (3.0%) despite clear margins on primary excision, most with margins of 1.4–3.5 mm. Regression was reported in 42.2% of primary excisions but showed no significant association with residual disease. Regression reporting was absent in one-third of pathology reports. Residual MIS following apparently complete excision is uncommon but not negligible. Our findings suggest that WLE may confer benefit for a small subset of patients, even when margins exceed 1 mm, although no subgroup at clearly increased risk was identified. While recurrence was not observed, limited follow-up precludes definitive conclusions. These data support informed, shared decision making and highlight the need for prospective, multicentre studies with standardized histopathological reporting.