DP17 Categorizing BAP1-inactivated melanocytic tumours using dermoscopic and clinical features with correlation to pathology

Abstract

BRCA1-associated protein-1 (BAP1)-inactivated melanocytomas (BIMs) are intermediate tumours. Although most occur sporadically, multiple BIMs may arise in patients with germline BAP1 mutations. Accurate clinical identification is important, as diagnosis of two BIMs qualifies patients for germline genetic testing and potential cancer screening. Yélamos et al. identified five common dermatoscopic patterns in BIMs (Yélamos O, Navarrete-Dechent C, Marchetti MA et al. Clinical and dermoscopic features of cutaneous BAP1-inactivated melanocytic tumors. J Am Acad Dermatol 2019; 80: 1585–9). However, correlation with pathology has not been explored. The aim of this study was to determine whether BIMs in our cohort conform to the dermoscopic categories of Yélamos et al. and to assess correlation with histopathological features. We retrospectively reviewed 30 BIMs from 19 patients (12 female and 7 male; median age 37 years). Five of seven tested patients have confirmed BAP1 germline mutations, and three patients contributed multiple lesions. Images were reviewed by four dermatology consultants with expertise in pigmented lesions, with consensus reached. Eighteen of the 30 BIMs (60%) were pink-brown papules/nodules. Fifteen of these 18 (83%) were low grade, compared with 3 of 8 BIMs (38%) with multiple components. Dermoscopic images were available for 24 BIMs. Twenty-one (88%) fit Yélamos’ categories, most commonly ‘structureless pink with peripheral radial vessels’ (42%). Three (13%) did not conform and demonstrated a distinct structureless blue area clinically and dermoscopically. Two additional lesions with clinical images exhibited only blue pigmentation. All five blue-pigmented lesions were high-grade BIMs or melanoma exhibiting multiple atypical histological features (e.g. more than two mitoses, atypical junctional component, perineural invasion, ki67 > 5%, NRAS mutation, TERT promoter). Blue pigmentation was absent from all low-grade BIMs. Seven further high-grade BIMs and one melanoma lacked blue pigmentation. Dermoscopy was available for four, all fitting into Yélamos’ categories. We describe a previously unreported dermoscopic pattern in BIMs, characterized by a distinct structureless blue area, which may indicate higher-grade disease. Awareness of clinical and dermoscopic patterns may aid early recognition and appropriate genetic referral.