Clinical Information: This 82 year-old male had a previous excision of a posterior helical rim lesion. He underwent a re-excision of the lesion.
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Discussion and answer
Diagnosis: Microscopically, sections from the re-excision show nests of atypical melanocytes, some spindle shaped, within the epidermis. Single atypical cells are seen within the epidermis extending to the surface. This lesion is present at the lateral inked resection margin. These features are consistent with an in situ melanoma. An invasive component is not seen. An intradermal nevus is seen underlying the melanoma in situ.
In situ melanoma is characterized by atypical melanocytes, singly and in nests, confined to the epidermis, usually the basal layer. A co-existing nevus is seen in 1/3 of melanomas. Surgical excision is adequate for treatment of melanoma in situ and a 0.5 cm resection margin is recommended.