Malignant melanoma developing in an area of palmoplantar keratoderma (Greither's disease)

We report a case of malignant melanoma arising on the hyperkeratotic sole of a patient with palmoplantar keratoderma (PPK). Hyperkeratotic lesions were also seen on the dorsa of both hands and feet and the extensor aspects of elbows and knees. The patient's PPK appeared to have been transmitted by an autosomal dominant gene. Histologically, the hyperkeratotic lesions showed acanthosis, marked hyperkeratosis without parakeratosis, and hypergranulosis. All the findings corresponded to those of Greither's disease with malignant melanoma.