Association of Weight-Bearing Activity and Prognosis of Plantar Melanoma: An Unanticipated Perspective

Background: In the development of plantar melanoma, it is suspected that mechanical stress caused by weight-bearing activities, such as walking, rather than ultraviolet exposure, may play a significant role, showing a concentrated prevalence in areas of the foot where weight-bearing actions are prevalent. However, research investigating whether such mechanical stress influences disease prognosis has been limited. This study was designed to investigate the association between weight-bearing activity and the oncologic outcomes of patients with plantar melanoma. Methods: Patients presenting primary foot melanoma without evidence of distant metastasis, who underwent surgical treatment from 2005 to 2022 were reviewed. They were divided into three groups based on the location of the melanoma: the weight-bearing-plantar, nonweight-bearing-plantar, and subungual/dorsal group and compared for the oncologic outcomes. Results: In total, 286 patients a mean age of 62.4 years were analyzed for a mean follow-up of 46 months, which included 168 (58.7%) in the weight-bearing-planar, 61 (21.3%) in the nonweight-bearing-plantar, and 57 (19.9%) in the subungual/dorsum. The baseline characteristics and pathologic staging, including Breslow thickness, were similar among the three groups. Surprisingly, in the comparison of oncologic outcomes, the nonweight-bearing-plantar group exhibited higher recurrence rates, especially for distant recurrence, and worse disease-free survival compared with the other two groups. This association remained significant after adjusting for other factors, including Breslow thickness, ulceration, and tumor staging. Conclusions: Our findings suggest that while weight-bearing activity may be associated with the occurrence of acral melanoma, it may not act as a worsening factor in the progression of plantar melanoma.