Dermatomyofibroma: report of two cases.

Dermatomyofibroma is a recently described, benign acquired cutaneous proliferation of fibroblasts and myofibroblasts. We report 2 additional cases, both in young women. The lesions measured 0.5 and 1.0 cm and were located on the breast and upper back. Follow-up at 8 months and 3 years revealed no evidence of recurrence. Both lesions exhibited a uniform population of spindle cells forming intersecting long fascicles with a tendency to horizontal orientation in the reticular dermis. Cytologic atypia was absent and mitotic figures were minimal or absent. Collagen was present as thin fibers separating individual cells and as thicker bundles between the fascicles. A fine reticulin network surrounded the spindle cells. Elastic fibers were mostly preserved and appeared thicker or even increased in number. The spindle cells were immunoreactive for vimentin and muscle actin and negative for desmin, S-100 protein, factor XIIIa, and CD34. Electron microscopic studies confirmed the presence of myofibroblasts. The differential diagnosis was made with cellular and fibrous dermatofibroma, piloleiomyoma, hypertrophic scar, and dermatofibrosarcoma protuberans, both classic and plaque type. The data presented supports the histologic distinction of dermatomyofibroma from other fibroblastic proliferations of the skin.