Density and distribution of acral melanocytic nevi and acral melanomas on the plantar surface of the foot

Acral melanoma (AM) is a distinct subtype of melanoma with unique clinical, morphologic, and genetic features. AM occurs on sun-protected skin, has a unique genetic profile with a lack of ultraviolet light signature mutations, a lower mutational burden, and a high number of copy number and structural changes.1 Unlike cutaneous melanoma (CM), AMs are rarely associated with nevi (≤11%).2 AMs are more common on certain weight-bearing areas of the feet in Japanese and white patients3, 4; acral melanocytic nevi (AMN) are more common on non–weight-bearing areas in Korean patients.5 If AMs evolve from AMN or an intermediate precursor, the location and incidence of AMs and AMN or atypical AMN should correlate. Herein, we compare the distribution of AMN and atypical AMN to the distribution of AM on the plantar surface of the foot in a predominately white population.

This study was approved by our institutional review board. A retrospective search of the pathology records was performed from 2000 to 2016 at Mayo Clinic. Two hundred and eighty-four cases met inclusion criteria: 1) biopsy-confirmed AM, AMN, or atypical AMN; 2) location on the plantar surface of the foot. A chart review was performed, and lesions were mapped by exact location and consolidated into weight-bearing (ie, heel, lateral midfoot, and forefoot) and non–weight-bearing (arch) regions. Age, distribution, and distribution uniformity were compared with the Kruskal–Wallis test, the Fisher exact test, and a chi-square goodness of fit test. The significance level was 0.05.