Understanding acral lentiginous melanoma: from the clinic to guidelines

Abstract

Invasive acral lentiginous melanoma (ALM) is a distinct melanoma subtype that primarily affects non-sun-exposed extremities, such as the palms, soles and nail beds. It is characterized by lentiginous proliferation of atypical melanocytes along the basal layer of glabrous skin. While ‘acral melanoma’ is a broad term referring to melanomas arising on acral sites, ‘acral lentiginous melanoma’ specifically refers to this lentiginous subtype. ALM is disproportionately represented among individuals with darker skin phototypes, including Black, Hispanic and Asian populations, in whom it accounts for a higher proportion of melanoma cases than in White populations. While it comprises just 2–3% of all melanomas, ALM has a poorer prognosis, with 5-year melanoma-specific survival rates averaging 80.6%. The pathogenesis of ALM remains incompletely understood. It is not primarily induced by ultraviolet (UV) radiation but is often associated with mechanical stress on weight-bearing or high-friction areas. Recurrent mutations in KIT, NF1, TERT and TP53 are also frequently observed, particularly in older and Asian patients, underscoring ALM’s distinct molecular profile. Diagnosis is often delayed due to its subtle presentation as irregularly pigmented macules or patches. Histologically, ALM demonstrates lentiginous basal proliferation with dermal invasion. Management typically involves wide local excision, although advanced disease may require lymph node surgery, radiotherapy or systemic treatment. Prognosis is influenced by tumour thickness, ulceration and sentinel lymph node involvement. Persistent disparities in outcomes highlight the need for greater awareness, earlier diagnosis and targeted management strategies to address the biological and sociodemographic complexities of ALM.