[Clinicopathologic and genetic studies of desmoid-type fibromatosis].

OBJECTIVE: To study the clinicopathological and genetic features of desmoid-type fibromatosis, and to investigate the feasibility of detecting trisomy 8 in formalin fixed, paraffin embedded (FFPE) tissue by fluorescence in-situ hybridization (FISH).

METHODS: A total of 96 cases were included in this study. All patients had clinical information. Histopathologic and immunohistochemical evaluations were available in 69 cases, and ultrastructural evaluation was done in 2 cases of desmoid-type fibromatosis. FFPE tissue sections were available in 20 tumors for the trisomy 8 detection by FISH.

RESULTS: There were 20 male and 76 female patients with ages ranging from 8 to 86 years (mean 35.3 years). Clinically, there were 44 extra-abdominal tumors, 28 abdominal wall tumors and 23 intra-abdominal lesions mostly involving the mesentery. Most cases presented with nodular or funicular masses with white firm cut surfaces, measuring 0.6 to 24.0 cm (mean 8.4 cm) in size. Histologically, desmoid-type fibromatoses showed longitudinal fascicles of spindle fibroblasts and myofibroblasts in a predominantly collagenous background. The tumor cells stained positive for vimentin, alpha-smooth muscle actin, desmin, and beta-catenin (47.8%, 33/69). Ultrastructurally, most tumor cells had features of fibroblasts, including rich endoplasmic reticulum and Golgi apparatus. Some tumor cells were myofibroblast-like cells exhibiting intercellular junctions, fibronexous junctions and stress fibers. Trisomy 8 was detected in 6 of 20 cases of desmoid-type fibromatosis including 5 of the 8 recurrent tumors but only one of the 12 primary tumors. The latter tumor also recurred three years later.

CONCLUSIONS: Desmoid-type fibromatosis is an intermediate (locally aggressive) tumor that occurs predominantly in young females. The lesion consists of fibroblasts and myofibroblasts with the latter showing characteristic features including stress fibers and fibronexous junctions. Trisomy 8 can be detected in FFPE tissue by FISH, and its presence serves as a useful predictor of tumor recurrence and may define a subtype of desmoid-type fibromatosis with high recurrence rate.