Malignant Fibrous Histiocytoma

A 45-year-old woman presented with a slowly enlarging, mildly tender lesion on the left sole. The large indurated plaque was studded with multiple firm papules and nodules that involved the instep and extended onto the medial aspect of the foot. There was no regional adenopathy.

The differential diagnosis included many benign dermal neoplasms, such as dermatofibroma and lipoma; malignant dermal tumors, including dermatofibrosarcoma, liposarcoma, and cutaneous metastases; extramedullary plasmacytoma, lymphoma cutis, and other cellular infiltrative processes; and deposition disorders, such as nodular mucinosis and amyloidosis. A biopsy revealed deeply infiltrating pleomorphic spindle cells with abundant, atypical mitotic figures. Immunohistochemical staining of the specimen suggested a histiocytic cellular origin; the tumor was classified as a malignant fibrous histiocytoma.

To maximize removal and minimize tissue loss to preserve form and function, Mohs micrographic surgery was used to excise the tumor. The patient is free of apparent disease 2 years postoperatively; she is examined regularly.