Prognosis of a deep excision margin within or beyond subcutaneous fat for invasive acral melanoma of the sole: A multi-institutional retrospective study.

Background: Preservation of plantar subcutaneous fat is crucial for cushioning in the surgical treatment of acral melanoma of the sole. However, no studies exist on the relationship between deep margins and prognosis. We aimed to retrospectively compare the prognoses of different deep margins (within or beyond the subcutaneous fat) in patients with invasive acral melanoma of the sole who underwent wide local excision.

Methods: In this multi-institutional retrospective study, survival was compared between 2 groups of patients: those with tumors excised within (S group) and those beyond the subcutaneous fat (D group).

Results: In total, 464 patients were included. Cox multivariable analyses showed that the depth of the deep excision margin was not associated with local recurrence-free survival, overall survival, or distant metastasis-free survival (hazard ratios of 1.20, P = .36; 1.10, P = .66; and 1.42, P = .05, respectively). However, excision beyond the subcutaneous fat was negatively associated with disease-free survival (hazard ratio 1.45, P = .02). After propensity score matching (both groups, n = 139), no significant differences were observed in survival outcomes between the S and D groups (5-year local recurrence-free survival: 72.8 vs 66.8%, P = .55; 5-year disease-free survival: 55.3 vs 43.7%, P = .24; 5-year overall survival: 76.2 vs 73.2%, P = .52; 5-year distant metastasis-free survival: 63.3 vs 54.1%, P = .13). Subgroup analysis of American Joint Committee on Cancer stages revealed no significant differences in survival outcomes between the 2 groups at any stage.

Conclusion: Wide local excision beyond the subcutaneous fat was not associated with survival benefit of acral melanoma of the sole. Excision within the subcutaneous fat may represent the optimal deep margin.