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.

Background Weightbearing areas of sole were reported to be significantly more vulnerable to melanoma than non-weightbearing areas. Few studies have investigated the role that mechanical stress plays in increasing the incidence of plantar melanoma (PM). Objective This study aims to investigate the potential role of mechanical stress in the formation of PM and evaluate the association of mechanical stress with certain pathological features of melanoma by using meta-analysis. Methods We analysed the distribution pattern of 72 PM lesions in Chinese patients and compared their incidence and demographic and clinicopathological features based on sites with different stress exposure. Results The most common region with a PM was the heel, followed by the forefoot, plantar aspect of the toes, lateral midfoot (LM) and arch. Both the heel and forefoot were significantly associated with a higher incidence of melanoma than the arch. A high density of lesions was observed in the posterior half of the heel and the lateral forefoot. Despite subtle differences in the contour maps of the density of lesions based on sex and age, different groups showed the same primary distribution tendency. The comparison between weightbearing and non-weightbearing areas revealed no significant difference in sex, age, lateralization, clinical pigmentation, Breslow depth or ulceration. However, the meta-analysis revealed that melanoma on weightbearing areas manifested as invasive melanoma at the time of diagnosis more frequently than cases on non-weightbearing areas (OR = 0.300 [95% CI, 0.092-0.977]; P = 0.046). Conclusion Weightbearing areas indicating mechanical stress are correlated with a higher number of plantar melanoma compared with non-weightbearing areas and also show a tendency to be involved by invasive melanomas at the time of diagnosis more frequently than non-weightbearing areas.