Margin involvement after the excision of melanoma in situ: The need for complete en face examination of the surgical margins

BACKGROUND The standard treatment for cutaneous melanoma in situ is surgical excision followed by standard pathologic evaluation. Serial cross-sectioning (bread-loafing) may result in false negative margin examination and higher local recurrence rates than Mohs micrographic surgery, which histologically evaluates the entire surgical margin. OBJECTIVE To estimate the sensitivity of bread-loafing in detecting residual melanoma in situ at surgical margins. METHODS A retrospective study was performed including 36 cases of melanoma in situ treated with Mohs surgery with positive margins after initial excision with 5 mm margins. The length of the margin involved with melanoma was measured. The ability of bread-loafing to detect residual tumor was calculated. RESULTS The average linear extent of tumor at the surgical margin was 1.4 mm. Bread-loafing at 1, 2, 4, and 10 mm intervals would have a 58, 37, 19, and 7% chance of detecting positive margins, respectively. In order to detect 100% of positive margins, bread-loafing would have to be performed every 0.1 mm. CONCLUSION Bread-loaf cross-sections through excised melanoma specimens are inherently unreliable for detecting residual melanoma at the surgical margins. We recommend complete histologic margin control of the entire surgical margin using en-face tissue orientation (Mohs technique) to reduce the risk of recurrence.