Collagenous fibroma (desmoplastic fibroblastoma): a report of seven cases.

We report the clinical features, light microscopic and ultrastructural appearance, and the immunohistochemical profile of seven benign fibrous tumors recently designated as desmoplastic fibroblastoma. The tumors occurred in four women and three men, who ranged in age from 41 to 76 years (mean, 53 yr). The tumors were located in the left thigh, right shoulder, right upper arm, left forearm, right neck, posterior neck, and foot and measured from 1.5 to 8 cm (mean, 4.6 cm) in greatest diameter. Four tumors were located in the subcutaneous tissue, two tumors were intramuscular, and one tumor involved the subcutaneous tissue and adjacent skeletal muscle. Six patients underwent a simple excision; one patient underwent a wide excision of the tumor. Grossly, the tumors were well circumscribed with a white to tan-white, bulging cut surface. Microscopically, they all displayed similar features and were composed of widely separated stellate- or spindle-shaped cells embedded in a hypovascular fibrous or fibromyxoid stroma. No mitotic figures, calcifications, or necrosis were identified. Five tumors were well demarcated, and two tumors had focally infiltrating margins. Ultrastructural examination performed on two cases showed that the tumor cells had features of fibroblasts and myofibroblasts. Immunohistochemical examinations performed on six cases showed that all of the tumors were diffusely positive for vimentin. One tumor showed diffuse staining for smooth muscle actin, and two tumors were focally positive for that antibody. One tumor showed diffuse staining for muscle actin, and another one was focally positive. Two tumors demonstrated diffuse faint staining for S100 protein. There was no staining for desmin, keratin, or CD34. Follow-up information was available in four cases and ranged from 1 to 60 months (average, 24 mo). No tumor recurred. Although the term desmoplastic fibroblastoma has been applied to this neoplasm, we think that the name collagenous fibroma is more appropriate for these tumors.