Mechanical stress on the plantar surface of the foot, which is typical of normal weightbearing on the foot, is associated with a higher formation of plantar melanoma compared with other non-weightbearing areas of the body. This is according to study data in the Journal of European Academy of Dermatology and Venereology.

The study investigators retrospectively examined data from a melanoma database at the Peking Union Medical College Hospital. In their review, researchers identified 107 cases of acral melanoma diagnosed between August 1991 and June 2017. Cases included melanomas diagnosed on the sole (n=64), toes (n=10), fingers (n=5), and subungual location (n=28). A total of 72 cases were considered plantar melanoma and were included in the final analysis. A meta-analysis that examined studies with data on pathologic parameters of plantar melanoma based on varying mechanical stress exposures was also performed.

The heel was the most common region with plantar melanoma, followed by the forefoot, plantar aspect of the toes, lateral midfoot, and arch. A higher proportion of manual laborers had plantar melanoma on weightbearing areas vs non-manual laborers (90.9% vs 78.6%, respectively). There was a higher observed density of lesions in the posterior region of the feet as well as in the lateral forefoot.

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Study investigators found no difference between weightbearing and non-weightbearing areas in sex, age, lateralization, clinical pigmentation, Breslow depth, or ulceration. According to the meta-analysis, melanomas on weightbearing regions were more frequently manifested as invasive melanoma at diagnosis compared with plantar melanoma cases on non-weightbearing regions (odds ratio, 0.300; 95% CI, 0.092-0.977; P =.046).

Limitations of the study included its single-center retrospective design as well as the inclusion of only a small number of study participants with plantar melanoma.

Based on their findings, the researchers speculate “that the mechanical stress load and duration in combination with histological and biomechanical features of the plantar soft tissue may play roles in the underlying mechanism by which mechanical stress promote the occurrences of” plantar melanoma.

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Reference

Gong HZ, Zhang S, Zheng HY, Qu T, Li J. The role of mechanical stress in the formation of plantar melanoma: a retrospective analysis of 72 Chinese patients with plantar melanomas and a meta-analysis [published online September 7, 2019]. J Eur Acad Dermatol Venereol. doi:10.1111/jdv.15933