ORIGINAL ARTICLE – MELANOMAS The Association Between Excision Margins and Local Recurrence in 11,290 Thin (T1) Primary Cutaneous Melanomas: A Case–Control Study Alastair D. MacKenzie Ross, MD, FRCS (Plast) 1,2 , Lauren E. Haydu, BSCHE, MIPH 1,3 , Michael J. Quinn, MBBS, FRACS 1,3,4 , Robyn P. M. Saw, MB, MS, FRACS 1,3,4 , Kerwin F. Shannon, MBBS, FRACS 1,3,4 , Andrew J. Spillane, MD, FRACS 1,3 , Jonathan R. Stretch, MBBS, DPhil(Oxon), FRACS 1,3,4 , Richard A. Scolyer, MD, FRCPA, FRCPath 1,3,5 , and John F. Thompson, MD, FRACS, FACS 1,3,4 1 Melanoma Institute Australia, North Sydney, NSW, Australia; 2 Department of Plastic Surgery, Guy’s and St Thomas’ NHS Foundation Trust, London, UK; 3 Sydney Medical School, The University of Sydney, Sydney, NSW, Australia; 4 Department of Melanoma and Surgical Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia; 5 Department of Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia ABSTRACT Background. At presentation, most primary cutaneous melanomas are ‘‘thin’’ (Breslow thickness B1 mm, desig- nated T1 in the American Joint Committee on Cancer staging system) and local recurrence (LR) is rare. Most current management guidelines recommend 1 cm surgical excision margins for T1 melanomas, but evidence to sup- port 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. Methods. From a large, prospectively collected, single- institution database, patients with primary cutaneous mel- anomas B1 mm 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. Results. From 11,290 primary melanomas B1 mm thick, 176 (1.56 %) cases with LR were identified and 176 con- trols (without LR) were selected. LR occurred after a median time of 37 months (range 3–306 months) 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 com- posed predominantly of spindle cells (p = 0.005). However, Breslow thickness, Clark level, ulceration, mitotic rate, regression, and lymphovascular invasion were not. Conclusions. LR was associated with \ 8 mm histologic excision margins (corresponding to \ 1 cm margins in vivo) and desmoplastic, acral, and lentigo maligna melanoma subtypes. This study provides evidence that a C1 cm clinical excision margin for thin (T1) primary melanomas reduces the risk of LR. Most patients who present with a primary cutaneous melanoma have a tumor that is thin (Breslow thickness B1 mm, designated T1 in the American Joint Committee on Cancer [AJCC] staging system for cutaneous mela- noma). 1,2 They have a good prognosis and a low rate of local recurrence (LR) and distant recurrence. 3 However, 8 % of patients with T1 melanomas die of their disease within 10 years, many of them after initial LR. 1,4 The reported prevalence of LR in patients with thin melanomas is low (Table 1). Randomized controlled studies of wide excision (WEx) margins for thinner pri- mary cutaneous melanomas have concentrated on T2 tumors. In the World Health Organization trial of 1 versus 3 cm excision margins for melanomas B2 mm thick, only four of 612 patients developed LR; all were T2. 5 In another trial assessing 2 versus 5 cm margins for melanomas \ 2.1 mm thick, there was only one recurrence (Breslow thickness 0.95 mm) in 159 patients with melanomas Ó Society of Surgical Oncology 2015 First Received: 23 March 2015 J. F. Thompson, MD, FRACS, FACS e-mail: john.thompson@melanoma.org.au Ann Surg Oncol DOI 10.1245/s10434-015-4942-0