malignant melanoma in situ
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ma·lig·nant mel·a·no·ma in si·tu
a melanoma limited to the epidermis and composed of nests of atypical melanocytes and scattered single cells extending into the upper epidermis; local excision is curative although the lesion, if untreated, may soon invade the dermis. Malignant lentigo may be considered a slowly progressive type of malignant melanoma in situ.