Seborrheic keratosis is a very common benign skin tumor in man. Melanoma is rare but is the most dreaded of all malignant skin tumors. A melanoma arising in a seborrheic keratosis is distinctly rare. We are reporting such a case occurring in an 86-year-old man.
An-86-year-old male with a history of multiple actinic keratoses and seborrheic keratoses of the head and trunk presented with a mid-back skin lesion. The lesion was poorly circumscribed, flat, and gray, with a pink-tan, well-circumscribed scaly nodule within it. The biopsied lesion was composed of the usual features of hyperkeratotic seborrheic keratosis, but with focal atypical melanocytic proliferation with nesting along the dermal-epidermal junction. We interpreted this lesion as a melanoma in-situ arising within a seborrheic keratosis.
It is not uncommon for many physicians to remove a typical seborrheic keratosis without a confirmatory microscopic confirmation. We urge that all such lesions be examined by the pathologist to avoid missing another concomitant malignant lesion such as melanoma which needs adequate resection and close follow-up.