Background: Collagenous fibroma (desmoplastic fibroblastoma) is poorly recognized and may be mistaken for other benign or even malignant spindle-cell tumors of soft tissue because of the small number of reported cases.
Design: Collagenous fibromas resected from four adult women were studied histologically and immunohistochemically.
Results: The tumors were well-circumscribed firm masses, measuring from 1.0 to 13.8 cm (mean, 5.5 cm) across the greatest diameter, located in the subcutaneous or deep soft tissue of the shoulder, thigh, back, and neck. Each of the tumors was characterized by a paucicellular lesion with spindle- and stellate-shaped fibroblastic cells embedded in a hypovascular, densely fibrous stroma. Mitotic figures and necrosis were not identified. One tumor contained dystrophic calcification and metaplastic bone, and another included small foci of floretlike multinucleated giant cells. Although appearing well demarcated on gross examination, one tumor focally infiltrated the surrounding skeletal muscle and adipose tissue. On immunohistochemical examination, all of the tumors were diffusely positive for vimentin. One tumor showed focal staining for alpha-smooth muscle actin, and another was partially positive for desmin, a staining profile that is typical of myofibroblasts. No tumor recurred during the follow-up periods of 67 to 108 months (mean, 93 months).
Conclusion: Collagenous fibroma may be a distinctive fibrous soft-tissue tumor with benign biological behavior.