Background: Lentigo maligna is an in situ malignant melanoma for which the treatment of choice is surgical excision. The current recommendation is local resection with a 0.5 to 1.0 cm margin of normal skin. Because many lesions occur on the face, the narrowest possible margin reduces the amount of scarring. Controversy surrounds the use of Mohs micrographic surgery to preserve normal skin and resect the lentigo maligna. Objective: The purposes of this prospective study were to determine the narrowest possible margin of resection of lentigo maligna and the accuracy of frozen and fixed histologic specimens from those margins. In addition, the benefit of adjunctive immunoperoxidase staining with antibodies to S-100 protein and HMB-45 monoclonal antibody was examined retrospectively. Methods: A Wood's light was used to delineate the clinical margin in 16 cases of lentigo maligna that were resected with serial excisions 0.3, 0.6, 1.0, and 1.3 cm from the clinical border of the tumor. Frozen sections were confirmed by fixed histopathologic specimens. Subsequently these tissue blocks were examined with antibodies to S-100 protein and HMB-45 monoclonal antibodies. Patients were observed 5 to 9 years. Results: One of the 16 patients had a recurrence 8 years after surgery. Although lesions with a diameter less than 2.0 cm had narrower margins of resection, the majority of lesions were resected with a margin of 0.6 to 1.0 cm. Lesions larger than 3.0 cm in diameter required a margin of resection greater than 1.0 cm. The antibody to S-100 protein was neither sensitive nor specific enough to assist with identification of the process. HMB-45 monoclonal antibody was sensitive and assisted in the identification of atypical melanocytes. Conclusion: The modifications of Mohs micrographic surgery including the use of fixed histopathologic specimens and the use of HMB-45 monoclonal antibody to help delineate atypical melanocytes offer the possibility of narrower margins of resection for lentigo maligna.
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