Desmoplastic malignant melanoma. A clinicohistopathologic study of 25 cases

A clinical and histologic review of 25 patients with melanocytic lesions classified as desmoplastic malignant melanoma is reported. All of the lesions were located in sun-exposed sites. The average age was 61.2 years (range, 38 to 83), with a median age of 56. There were 14 female and 11 male patients. Desmoplastic malignant melanoma is a melanocytic and fibroblastic proliferation that occurs predominantly in the head and neck area. The bland constituent cells resemble fibroblasts and are often arranged in bundles or fascicles, which may be arrayed perpendicularly to the overlying epidermis. Enlarged and/or atypical cells are usually scattered among the spindled cells. Most, but not all, of the tumors (24 of 25 in this series) are associated with lentigo maligna or an atypical junctional melanocytic proliferation. Mitotic figures are always found within the constituent cells of the fibrous-appearing mass, and neurotropism may be present. Patients with desmoplastic melanoma typically present with a mass, which is occasionally associated with a pigmented lesion. The lesions in our series were deeply invasive to level IV or V. Lentigo maligna and a dermal fibroblastic-appearing mass containing atypical cells arranged in fascicles are the most common morphologic features found in desmoplastic melanoma. Follow-up data is available for 23 patients. The average length of follow-up was 2.7 years (range, 0.1 to 9 years). Eighteen patients were observed for 3 or more years. Twelve patients developed local recurrences, and five developed metastases; three of the patients with metastases had a local recurrence before the development of metastases. Three of the patients with metastatic melanoma died of tumor between 2 and 4 years after their initial excision. Eight of the 12 locally recurring lesions were either diagnosed initially as a benign lesion or histologic examination was not performed on the initial excision specimen. It appears that recurrence may be related to inadequate initial therapy.