Abstract

One of the modalities for surgical management of melanoma in situ (MIS) involves the “square” procedure (SP) in which 2-3 mm strips of skin surrounding a biopsy proven MIS are excised and submitted en-face for permanent-section histologic analysis. In this study we aimed to evaluate the feasibility and effectiveness of the SP technique from a pathology perspective on a cohort of 192 patients from our institution. Majority of the lesions involved the head & neck (52%) followed by extremities (26%), trunk (20%) and acral (3%) and the most common diagnosis was MIS lentigo maligna type (63%). Overall 28% and 22% of cases had positive margins in the first and second round of excision, respectively. Frequent diagnostic problems included differentiating melanocytic hyperplasia of sun-damaged skin from periphery of melanoma requiring Mart-1 stains in 5% of SP skin strips examined and incomplete sectioning of epidermis due to challenges in tissue processing of the skin strips requiring deeper levels in 23%. In 26 cases (52%) with positive margins on the first SP there was no residual MIS in the excision specimen, indicating the possibility that some of the SP margins interpreted as positive were melanocytic hyperplasia. Also in two cases the excision had positive margins with MIS/atypia although the initial SP margins were negative, likely due to regression. Our results indicate that while SP is a valuable clinical technique, histopathologic examination of SP specimens is challenging and requires specialized expertise for both the pathologist and the histology laboratory.