Desmoplastic fibroblastoma

Previous reports of a distinctive, fibrous, soft-tissue tumor include eight patients with subcutaneous lesions and six patients with intramuscular lesions. We report a 48-year-old woman with a 2-cm cutaneous and subcutaneous nodule on the left arm with the same histologic features. An excisional biopsy showed a large, well circumscribed tumor replacing the reticular dermis and subcutaneous tissue. The tumor was relatively hypocellular and composed primarily of large, spindled, plump or stellate fibroblasts haphazardly dissecting between thickened fibrotic collagen bundles. The stroma contained a large amount of mucin which was positive with alcian blue at pH 2.5, and relatively numerous mast cells were present. The fibroblastic-like cells were positive with Vimentin and Factor XIIIA and negative with S-100, desmin, actin and keratin.