Plexiform fibrohistiocytic tumor: Clinicopathologic analysis of 22 cases

Twenty-two cases of plexiform fibrohistiocytic tumor were reviewed to perfo rm a clinicopathologic correlation with the behavior of the neoplastic enti ty. The tumor arises more frequently in children, adolescents, and young ad ults (mean age of presentation, 14.6 years), with strong female predilectio n (F:M, 6:1). It involves preferentially the upper extremity (64%), especia lly the fingers, hand, or wrist (45%). Most patients present with a small ( average size, 2.5 cm; range, 0.5-8 cm) painless mass that slowly enlarges f or months to years. All tumors involve subcutaneous adipose tissue, with ex tension into the dermis (19%), skeletal muscle (14%), or both (14%). Grossl y, the tumors characteristically are poorly circumscribed and of firm consi stency. Histologically, they are characterized by a plexiform proliferation of mononuclear histiocyte-like cells, multinucleated osteoclast-like cells , and spindle fibroblast-like cells in variable proportions and have three distinct growth patterns: fibrohistiocytic (36% of tumors), fibroblastic (3 2%), and mixed (32%), depending on the predominant cell type. Cellular atyp ia and pleomorphism are usually absent or minimal. Most tumors (78%) displa y mitotic activity, frequently <3 mitoses/10 high power fields, and only 14 % of the lesions display atypical mitoses, Vascular invasion was seen in on ly one tumor. Immunohistochemically, all tumors evaluated reacted with anti bodies to CD68 that stained mainly the multinucleated giant cells and, to a lesser extent, mononuclear histiocyte-like cells and, occasionally, fibrob last-like cells. Less frequently, staining with antiactin antibodies was ob served, restricted mainly to spindle cells. All nine tumors examined had a diploid DNA content. According to latest follow-up data (average period, 3. 6 years) from 16 patients, 13 (82%) were alive with no evidence of disease (average, 3.6 years), 1 (68) was alive with metastatic disease (follow-up, 2.3 years), 1 (6%) was alive with a stable pulmonary nodule of unknown natu re (follow-up, 1.75 years), and 1 (6%) had died of disease 3 years after lo cal recurrence and regional lymph node and pulmonary metastases developed. Two patients (12.5%) had local recurrence, 1 (6%) had regional lymph node m etastasis, and 3 (19%) had pulmonary metastases. No proven association betw een clinicopathologic features and outcome was identified. In conclusion, p lexiform fibrohistiocytic tumor is a rare mesenchymal neoplasm of young per sons characterized by low-grade malignant behavior and is prone to recur lo cally and occasionally to metastasize regionally and systemically.