Confocal microscopy, dermoscopy, and histopathology features of atypical intraepidermal melanocytic proliferations associated with evolution to melanoma in situ.

BACKGROUND Atypical intraepidermal melanocytic proliferations (AIMP) is a descriptive term sometimes applied to biopsies that do not fulfill diagnostic criteria of melanoma. They are common on sun-damaged skin, but their definition and management are controversial. OBJECTIVE To describe dermoscopic (DS), reflectance confocal microscopic (RCM) and histopathological features of AIMP and identify features associated with subsequent melanoma in situ (MIS). METHODS A retrospective analysis of AIMP lesions correlated with patient outcome at two melanoma tertiary centers between 2005 and 2015. RESULTS Thirty-four patients were included. Nine (26%) patients had MIS in subsequent biopsies. Predictors of later MIS were target-like pattern (OR:12.0 [CI: 1.23, 117.41]; P = 0.032) and high-density vascular network (OR:12 [CI: 1.23-117.41], P: 0.032) on DS, and presence of dendritic cells touching each other (OR:9.1 [CI: 1.54, 54.59], P = 0.014) on RCM. Clinical predictors of worse outcome included a previous history of MIS at the same site. Radiotherapy for AIMP had a high failure rate (all patients presented with recurrent disease, three as AIMP and two as MIS). CONCLUSIONS Considering that most cases in this series received non-surgical treatment at baseline, we recommend close monitoring for lesions with target-like pattern and density vascular network on DS and treatment for lesions with progression of atypia and/or with "confluent" dendritic cells on RCM. Although the number of patients in this series is very low, early surgery is recommended for MIS cases that recur as AIMP.