Acral melanoma in the Caucasian population: a comprehensive cohort study on epidemiological, clinicopathological, and prognostic features.

Background: Acral melanoma is associated with poor prognosis. Studying the characteristics and prognosis of Caucasian patients is crucial to understand the distinct features of this tumor.

Objectives: To analyze the epidemiological, clinicopathological, and prognostic features of acral melanoma in Caucasian patients.

Methods: We conducted a retrospective, multicenter, cohort study of acral melanoma from a database across 20 hospitals from South Europe from January 2000 through December 2019.

Results: A total of 733 acral melanomas were identified (median age, 67.5 years; 95.2%, Caucasians; 77.5% of which were located on the feet). Overall, 77.5% of cases were invasive melanomas. Foot melanomas had a higher proportion of invasive cases (80.8% vs 69.8%; p = 0.003), stages III and IV at diagnosis (24.8% vs 11.7%; p < 0.001), thicker Breslow depth (2.8 mm vs 2.0 mm; p = 0.021) and a higher rate of positive sentinel lymph node biopsy (SLNB) (30.7% vs 15.7%; p = 0.012). Thicker Breslow depth and later age of onset were risk factors for melanoma-specific survival. Thicker Breslow depth and ulceration were independent prognostic factors of relapse-free survival. Melanoma location and histopathological subtype were not associated with worse prognosis. Recurrences were a common finding (27.7%), with distant metastases appearing earlier than locoregional recurrences (1.32 years [IQR, 1.12-1.87] vs 2.14 years [IQR, 1.68-2.70]; p = 0.015).

Conclusion: This study, the largest in a predominantly Caucasian population, underscores the unfavorable outcomes of acral melanoma. Foot melanomas exhibited delayed detection, increased invasiveness, thicker Breslow depth, increased SLNB involvement, and higher AJCC stages. The high recurrence rate and early distant metastases emphasise the critical role of intensive follow-up and routine imaging modalities to detect asymptomatic relapses.