A middle-age man with previous melanoma-in-situ of the back presents with new chin lesion biopsied as melanoma-in-situ on a deep shave biopsy. Subsequent surgical excision with 2 mm margins revealed no evidence of residual melanoma. Observation was chosen as the course of management. Should additional wider margin resection be performed?
Melanoma-in-situ (MIS) is a high risk lesion due to three primary reasons. The first is that a partially biopsied melanocytic lesion with a diagnosis of MIS tends to be a heterogeneous melanocytic lesion with a risk of invasive melanoma in other parts of the lesion. The second reason is atypical melanocytes can extend several centimeters beyond the clinical lesion. This is what accounts for a recurrence rate between 5-30% depending on the length of follow-up. Finally, a melanoma-in-situ itself has a transformation rate of 5-30% into melanoma.