Morphologic Spectrum of Desmoid-Type Fibromatosis

Objectives: Desmoid-type fibromatosis is a locally aggressive neoplasm composed of long sweeping fascicles of bland fibroblasts/myofibroblasts. Tumors with classic features are easy to identify, but the morphologic spectrum of this entity spans beyond the conventional histologic pattern. Since sampling of an unrecognized histologic variant may lead to misdiagnosis, especially on small needle biopsy specimens, we sought to fully characterize the morphologic spectrum of this entity. Methods: We examined 165 cases ofdesmoid-type fibromatosis and catalogued the morphologic patterns and percentage of those patterns identified in each case. Clinicopathologic variables, including age, sex, location, and recurrence, were analyzed and correlated with pattern frequency. Results: Seven morphologic patterns were identified, including conventional, hyalinized/hypocellular, staghorn vessel, myxoid, keloidal, nodular fasciitis-like, and hypercellular. The mean number of patterns per case was two, but some cases harbored up to five patterns. The greatest morphologic variability was seen in the intra-abdominal lesions, with these tumors having a significantly higher percentage of the keloidal and staghorn patterns compared with extra-abdominal and abdominal wall sites. No significant correlation between patient outcome (recurrence) and presence of variant morphologic pattern was observed (P = .549). Conclusions: The morphologic spectrum of desmoid-type fibromatosis is deceptively broad, and awareness of the variety of histologic patterns is critical for accurate diagnosis.