Track: Case Reports

Abstract:

Introduction 

Acral lentiginous melanoma (ALM) is a rare, aggressive variant of melanoma that disproportionately affects patients with skin of color. In recent years, a growing clinicopathologic dilemma has emerged describing an indolent, slow-growing ALM subtype ALM characterized by pigmented lesions clinically suspicious for melanoma but with incongruent bland findings on histopathology.

Case Series

Case 1: A 55-year-old African-American female presented with a 7-cm asymmetric brown patch on the left heel with irregular pigment networks distributed along acral furrows and ridges. Three scouting punch biopsies revealed slightly increased non-confluent, hyperchromatic melanocytes irregularly distributed along the basal layer.  The atypical melanocytes expressed SOX-10, Melan-A, and preferentially expressed antigen in melanoma (PRAME). The lesion required 4 consecutive stages of slow Mohs micrographic surgery to achieve clear margins.

Case 2: A 52-year-old African-American female presented with a 2.5-cm asymmetric, irregularly-bordered multi-toned brown patch at the plantar fifth metatarsophalangeal joint. She had undergone two consecutive biopsies three months prior, both inconclusive. A third biopsy (two scouting locations) was performed and demonstrated intraepidermal proliferation of angulated and hyperchromatic dendritic melanocytes at the basal layer with focal pagetosis. The atypical melanocytes expressed MiTF, Melan-A, and PRAME. The patient underwent wide local excision.

Discussion

Fewer than 30 cases of ALM in situ, indolent subtype have been reported. These pigmented lesions are clinically highly suspicious for ALM but lack classical features of architectural disorder and cytologic atypia. Instead, lentiginous proliferations of banal-appearing melanocytes are frequently observed. In this context, IHC staining – particularly with PRAME – can be critical.