DP18 Debunking the mystery of melanocytomas: a 9-year case series

Abstract

No practical recommendations exist for managing ‘melanocytomas’. These encompass ‘intermediate’-stage melanocytic tumours and have unclear optimal treatment and prognosis. We retrospectively analysed the demographics and management of 21 patients with melanocytoma in our region (May 2016 to August 2025). The median age at diagnosis was 43.5 years (range 17–72) and the cohort was predominantly female (16 female and 5 male). Lesions most commonly affected the extremities (n = 11, 52%), they measured on average 7 × 6 mm and they had a mean duration of 6 months (range 1–60). Most were referred as urgent suspected cancer (n = 16, 76%) and managed by dermatology (n = 18, 86%). All patients had Fitzpatrick skin type I or II (n = 21, 100%), and 3 (14%) had a history of melanoma. The prevalent prehistology diagnosis was melanoma (n = 10, 37%), with melanocytoma noted once (4%) as a differential, indicating frequent misdiagnosis. Histopathology confirmed the following 2023 WHO melanocytoma subtypes: 8 (38%) pigmented epithelioid, 6 (29%) BAP-1 inactivated, 5 (24%) Spitz, 2 (10%) WNT activated, and 0 MITF pathway activated. Invasions were mostly at Clark levels III (45%) and IV (55%). Next-generation sequencing was performed in three cases, identifying one high-risk Spitz melanocytoma with a RASAL2::RAF1 fusion; the others were unremarkable. Ultrasound of regional lymph nodes was negative in four patients (19%). All melanocytomas were surgically excised, with a median margin of 2 mm (range 1–3). Most cases (n = 20, 95%) were discussed at a multidisciplinary team meeting, and 16 cases (76%) had wide local excision, with a median surgical margin of 10 mm (range 3–10). No recurrence or metastasis occurred. The median ­follow-up duration was 6.2 months; one patient died from cardiac arrest. This study highlights the central role of histopathology in distinguishing melanocytoma from melanoma and emphasizes the need for standardized management guidelines. Adoption of ESP, EORTC and EURACAN expert recommendations may help harmonize diagnostic, surgical and follow-up practices for this challenging tumour group.