Lentigo maligna: defining margins and predictors of recurrence utilizing clinical, dermoscopic, confocal microscopy and histopathology features

Abstract Background Lentigo maligna (LM) is a subtype of melanoma in situ with poorly defined margins and a high recurrence rate. The biological behaviour of LM appears to differ widely between cases, from biologically indolent to biologically active variants, with some patients experiencing multiple recurrences. It is not known whether this is secondary to inadequate margins, field cancerization or the innate biology of the lesion itself. Objectives (a) Describe the margins of LM in detail by analysing LM in three zones, that is centre, edge and surround using reflectance confocal microscopy (RCM) and histopathology; (b) ascertain association of histological distance of LM and atypical melanocytic hyperplasia from the surgical margin with multi‐recurrent (MR) disease and (c) identify features (clinical, dermoscopy, RCM and histopathology) associated with MR LM. Methods (1) Descriptive observational study comparing the centre, edge and surround of LM on histopathology and RCM; (2) retrospective cohort study comparing parameters associated with MR and non‐recurrent (NR) LM. Results 30 patients (median follow‐up time 6.2 years) were included. On histopathology, confluent or near confluent lentiginous proliferation, melanocyte density >15 per 0.5 mm and adnexal spread were best for distinguishing surround from edge of LM. On RCM, predominant melanocytes, lentiginous proliferation and pleomorphism distinguished surround from centre/edge. MR patients had a median histological distance of LM from the surgical margin of 2mm (versus NR patients with an average distance of 4mm). MR patients had a greater proportion of more florid features, compared with NR on histopathology at both the centre and the edge but were similar in the surround. Conclusion These data may help pathologists and confocalists better define margins of LM. More florid features in MR patients, despite a similar background of sun‐damaged skin, suggest the innate biology of the lesion rather than the field of cancerization may explain MR LM.