Desmoplastic fibroblastoma (collagenous fibroma) is a benign fibrous tumor that presents as a slow-growing, painless mass. The usual sites of involvement are subcutaneous tissue or skeletal muscles of upper or lower extremities. Most patients are adults and it is more common in males (M:F=3-4:1). Grossly, it is firm, well-circumscribed with a white or gray homogenous surface without hemorrhage or necrosis. It is a hypocellular lesion composed of bland spindle or stellate cells in a collagenous background. There is no necrosis or increased mitotic activity. SMA and MSA are focally positive where as desmin, CD34, S-100 protein, and cytokeratins are negative. Some cases show translocation involving 11q12, similar to those seen in fibroma of tendon sheath. The differential diagnosis includes neurofibroma, calcifying fibrous pseudotumor, fibromatosis, low-grade fibromyxoid sarcoma, elastofibroma, and nodular fasciitis. Simple resection is curative treatment. There are no reports of recurrences or metastases. Ref: Enzinger & Weiss’s Soft Tissue Tumors, Sixth Edition, 2014; p. 229-231. Updated: May 3rd, 2017.