COLLAGENOUS FIBROMA (DESMOPLASTIC FIBROBLASTOMA) - A CLINICOPATHOLOGICAL ANALYSIS OF 63 CASES OF A DISTINCTIVE SOFT-TISSUE LESION WITH STELLATE-SHAPED FIBROBLASTS

Sixty-three cases of collagenous fibroma (desmoplastic fibroblastoma) from the files of the Armed Forces Institute of Pathology were analyze d. These tumors occurred mostly in men (80%) with a median age of 50 y ears (range, 16 to 81 years). The lesions had a wide anatomic distribu tion and involved the arm (24%), shoulder girdle (19%), posterior neck or upper back (14%), feet or ankles (14%), leg (14%), hand (8%), and abdominal wall and hip (6%). The patients typically presented with a h istory of a painless, slowly growing mass, often of relatively long du ration. The tumors ranged in size from 1 to 20 cm (median, 3.0 cm). Th e lesions were predominantly subcutaneous, but fascial involvement was common, and 27% of cases involved skeletal muscle. Gross examination typically showed an elongated, lobulated, or disc-shaped mass with a f irm consistency and a homogeneous pearl-gray color. Histologically, th e tumors often appeared well marginated on low-power examination, but most (78%) infiltrated fat or, less commonly, skeletal muscle. The les ional cells were relatively bland stellate and spindle-shaped fibrobla sts separated by a collagenous or myxocollagenous matrix. Mitotic acti vity was absent or minimal. Some of the lesional cells had a myofibrob lastic immunophenotype, as evidenced by focal reactivity for muscle-sp ecific and cu-smooth muscle actins. In a few cases, rare actin-positiv e cells were also positive for keratins. Desmin, S100 protein, and CD3 4 were not expressed. None of the 39 patients with follow-up (median, 11 years) developed a recurrence. Collagenous fibroma is a benign fibr oblastic/myofibroblastic proliferation. The large size of some of thes e tumors coupled with slow growth and persistence favors a neoplastic process over a peculiar reactive proliferation. The differential diagn osis includes a variety of reactive and neoplastic fibroblastic lesion s, most importantly fibromatosis and low-grade fibromyxoid sarcoma. Si mple, conservative excision is the treatment of choice for collagenous fibroma. Copyright (C) 1998 by W.B. Saunders Company.