Low-grade fibromyxoid sarcoma: a clinicopathologic study of 33 cases with long-term follow-up.

Cases listed in the U.T.M.D Anderson Cancer Center files as low-grade fibromyxoid sarcoma and originally diagnosed before 2004 were reviewed. They were included in the study if the diagnosis was confirmed and if there was adequate histologic material and clinical information with at least 5 years of follow-up. Thirty-three cases met the study criteria. The patients were 6 to 52 years old at the time of diagnosis (median, 29 y); 19 were male and 14 were female. The most common tumor locations were the shoulder area (5), thigh (5), and inguinal area (4). Tumor size varied from 1.5 to 16 cm (median, 9.4 cm) in those cases in which it was known. The typical histologic findings were contrasting fibrous and myxoid areas, moderate to low cellularity, bland-appearing spindle cells with no or slight nuclear pleomorphism and rare mitotic figures, and a swirling, whorled growth pattern. Prominent vascularity in myxoid areas and perivascular hypercellularity were fairly common, whereas larger hypercellular zones were sometimes seen in primary tumors but were more frequent in recurrences (local) and metastases. Hypercellular regions sometimes had round rather than spindle cells, a diffuse sheet-like cell arrangement, and/or a somewhat increased mitotic rate. Very hypocellular fibrotic areas were also observed and sometimes had thick collagen bundles. Pericollagenous rosettes were present in 6 cases but not in all specimens from these. Other growth pattern variations included storiform, fascicular-herringbone, and patternless areas; uncommonly noted were cell clusters, strands, palisades, and a retiform network. Additional unusual features were moderate nuclear pleomorphism (seen mostly in recurrent and metastatic tumors), cysts, osseous metaplasia, and a tigroid pattern with alternating fibrous and myxoid strips. One patient had a recurrence with features of sclerosing epithelioid fibrosarcoma, whereas 2 had dedifferentiated recurrences with anaplastic predominantly round cells and numerous mitotic figures. Fourteen patients died of tumor after 3 (this patient's tumor became dedifferentiated) to 42 years (median, 15 y). Nineteen patients were alive at last follow-up of 5½ to 70 years (median, 13 y), 6 with tumor and 13 without. Twenty-one patients had recurrence after intervals of up to 15 years (median, 3½ y), and 15 had metastases (mostly in the lungs and pleura) after periods of up to 45 years (median, 5 y). Except for dedifferentiation, which led to short survival after it occurred, histologic differences were not related to tumor behavior or patient survival. The 4 patients whose neoplasms measured <3.5 cm were all tumor free at last follow-up.