Abstract:

Desmoplastic fibroblastoma (collagenous fibroma) is a rare soft tissue tumor than usually arises in the subcutis or skeletal muscle. Desmoplastic fibroblastoma can cause diagnostic difficulty and we have seen a number of cases in consultation. Of the 20 cases we have received in consultation, 15 had available material to review. The patients had a mean age of 48 years (range 12-76; 3M:2F). There was a wide anatomic distribution, with tumors involving the head and neck (4/15; 27%), feet (3/15; 20%), lower extremities (2/15; 13%), back (2/15; 13%), shoulder (1/15; 7%), axilla (1/15; 7%), hand (1/15; 7%), and breast (1/15; 7%). The tumors involved the dermis to subcutis. The tumors ranged in size from 0.4 to 5.0 cm (median, 1.5 cm). All were hypocellular proliferations of bland stellate to spindled fibroblasts set in collagenous to focally myxoid stroma. By immunohistochemistry, SMA was positive in 3/5. None were positive for CD34 (0/5), EMA (0/5) or S100 (0/7). The differential diagnosis of desmoplastic fibroblastoma is varied and includes nerve sheath tumors, such as a neurofibroma or perineurioma, low-grade fibromyxoid sarcoma (LGFMS), fibromatosis, nodular fasciitis, and fibroma of tendon sheath. Diagnostic considerations from the contributors included spindle cell lipoma, nodular fasciitis, chondromyxoid fibroma, and low-grade fibromyxoid sarcoma. Desmoplastic fibroblastoma is less cellular than all of the entities in the differential diagnosis, and immunohistochemical stains can resolve the differential considerations in most entities (e.g. MUC4 in LGFMS). Recognition of the characteristic stellate cells in a hypocellular collagenous tumor and knowledge that desmoplastic fibroblastoma may present as a superficial tumor should prompt consideration of this diagnosis.

Financial Disclosure:
No current or relevant financial relationships exist.

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Gabriel Oaxaca, MD