DS06: It might be NICE, but do we need to change the way we approach melanoma in situ?

Hayley Smith and Walayat Hussain

Leeds Teaching Hospitals, Leeds, UK

Our management of melanoma in situ (MIS) is to ensure a 5-mm clinical margin, regardless of histological clearance after initial excision. We have established similar practice across the UK, confirming that the interpretation of National Institute for Health and Care Excellence (NICE) recommendations is confusing. The optimal clinical and histological margins required to prevent recurrence remains poorly understood. Furthermore, guidance considers MIS a single entity, despite different morphological subtypes, with little consideration for lesion site. We identified all MIS diagnosed between January 2015 and June 2021, including lentigo maligna (LM). Cases of MIS with histological clearance after initial excision and those with residual MIS following further surgery were identified. We compared lesions on the head and neck to those elsewhere. In total, 424 cases were identified (224 women and 200 men aged 21–98 years). Altogether, 302 lesions were on the trunk and limbs (19 were LM). Twenty-six lesions in the ‘below neck’ group were diagnosed on biopsy, with 276 diagnosed after initial excision. Of these, 254 (92%) were histologically excised with a margin of at least 1 mm. In total, 204 (80·3%) of these underwent re-excision, with the majority offered a 5-mm wide local excision (WLE). All re-excised lesions showed scar tissue only, regardless of the re-excision margin. Ninety-one of the 122 lesions in the head and neck region were LM (75 diagnosed on biopsy). Forty-seven were diagnosed on initial excision. Of these, 36 (76·6%) were considered completely excised with a histological margin of at least 1 mm. Twenty-four (66·6%) of these underwent re-excision with the majority offered 5-mm WLE. Ninety-two per cent of these showed scar only on re-excision, with no residual MIS, regardless of re-excision margin. One lesion had a focus of LM and one had a 0·1-mm margin. Both lesions were located on the ear. No recurrences have been reported in our cohort, with histologically clear margins of at least 1 mm, regardless of site. The majority of head and neck lesions were LMs. These typically occur in the context of sun-damaged lentiginous skin; therefore, we acknowledge the difficulties in histological margin control in this cohort. However, the majority of MIS below the neck are not lentiginous in morphology. Our data, one of the largest reviews of MIS in the UK, suggest the reliability of histological assessment in these lesions. We propose that nonlentiginous MIS below the neck with a histological margin of at least 1 mm be considered adequately treated, regardless of initial clinical margin. This approach will prevent further unnecessary surgical intervention in such patients.