The Association Between Excision Margins and Local Recurrence in 11,290 Thin (T1) Primary Cutaneous Melanomas: A Case-Control Study.

Abstract

At presentation, most primary cutaneous melanomas are "thin" (Breslow thickness ≤1mm, designated T1 in the American Joint Committee on Cancer staging system) and local recurrence (LR) is rare. Most current management guidelines recommend 1cm surgical excision margins for T1 melanomas, but evidence to support this recommendation is sparse. We sought to identify clinical and pathologic factors associated with LR in patients with T1 melanomas that might guide primary tumor management. From a large, prospectively collected, single-institution database, patients with primary cutaneous melanomas ≤1mm thick diagnosed between 1970 and 2011 who developed LR were identified and matched with controls. Clinical and pathologic parameters were analyzed for their association with LR. From 11,290 primary melanomas ≤1mm thick, 176 (1.56%) cases with LR were identified and 176 controls (without LR) were selected. LR occurred after a median time of 37months (range 3-306months) and was associated with narrower excision margins (hazard ratio=0.95, 95% confidence interval 0.92-0.98, p=0.001), desmoplastic, acral, and lentigo maligna melanoma subtypes (p=0.008), and melanomas composed predominantly of spindle cells (p=0.005). However, Breslow thickness, Clark level, ulceration, mitotic rate, regression, and lymphovascular invasion were not. LR was associated with <8mm histologic excision margins (corresponding to <1cm margins in vivo) and desmoplastic, acral, and lentigo maligna melanoma subtypes. This study provides evidence that a ≥1cm clinical excision margin for thin (T1) primary melanomas reduces the risk of LR.