Background: The clinicopathological and survival profiles across primary sites in acral melanoma (AM) are still controversial and unclear.
Methods: This is a multi-center retrospective study. Clinicopathological data of AM patients diagnosed between 1 January 2000 and 31 December 2017 from 6 large tertiary hospitals in China were extracted. Chi square tests were used to compare basic characteristics between primary sites of sole, palm and nail bed. Melanoma-specific survival (MSS) differences based on primary sites were compared by log-rank tests and multivariate Cox regressions were used to identify prognostic factors for MSS.
Results: In total, 1157 AM patients were included. The sole group had a more advanced initial stage, deeper Breslow thickness, higher recurrence rate and distant metastases risk (all P < 0.05). The proportion of age < 65 years and ulceration were statistically lower in nail bed and palm groups, respectively. A total of 294 patients underwent sentinel lymph node biopsy and rates of positive SLN status had no statistical difference across primary sites. Among 701 patients with genetic profiles, the mutational frequency of BRAF, C-KIT, and PDGFRA were similar except for NRAS (higher in sole group, P = 0.0102). The median MSS of sole, nail bed and palm patients were 65.0 months, 112.0 months, and not reached, respectively (log-rank P = 0.0053). In multivariate analyses, primary site, initial stage, ulceration and recurrence were the prognostic factors for MSS in overall population, but the statistical significance varied over primary sites.
Conclusions: Substantial clinicopathological and survival heterogeneities exist across different primary sites in the AM population. Sole melanoma has worse prognosis compared with palm and nail bed subtypes.