[457] Ossifying Fibromyxoid Tumor and Its Non-Ossifying Variant: A Diagnostic Challenge for Dermatopathologists

Darya Buehler, Natasha Atanaskova Mesinkovska, Colt M McClain, Brian P Rubin, John R Goldblum, Steven D Billings. Cleveland Clinic, Cleveland, OH; Vanderbilt University, Nashville, TN

Background: Ossifying fibromyxoid tumor (OFMT) is a rare, potentially aggressive, tumor that typically arises in the subcutis. Therefore it is encountered by dermatopathologists and is a source of diagnostic difficulty. In this study, the clinicopathologic features and outcomes of twenty-three subcutaneous OFMT were reviewed.
Design: Histologic sections of subcutaneous OFMTs were assessed for the morphologic patterns. Prognostic classification as typical, atypical and malignant OFMT was assigned. Patient and tumor characteristics and follow up information were obtained from institutional records and contributing pathologists.
Results: Patients (15 F, 8 M) ranged in age from 26 to 88 years (mean 53 years). The tumors ranged from 0.8 to 8.5 cm (mean 2.7 cm) in size, and all arose in the subcutis of the leg (n=11), trunk (n=7), head/neck (n=3), or arm (n=2). All were well circumscribed with a fibrous pseudocapsule. A partial shell of bone was present in 11 of 23 cases while 12 cases were classified as the nonossifying variant. All had a lobular growth pattern with the tumor cells arranged in combinations of nested, reticular and fascicular patterns. Cellularity ranged from low (n=13) to moderate (n=6) to high (n=4). Mild to moderate cytologic atypia was observed in most cases with more cellular cases demonstrating greater nuclear atypia. The average mitotic rate was 6 per 50 HPFs (range 0-46). 13 of 19 cases were positive for S100; focal desmin (4/12) and actin (2/14) immunoreactivity was also observed. One case co-expressed focal cytokeratin and CD10, and one case was positive for p63. Two cases met histologic criteria for malignant OFMT, having at least two of the following three features: increased cellularity, nuclear atypia and mitotic rate >2/50 HPFs, and two other cases were considered atypical. The spectrum of cytologic features was similar in both ossifying and non-ossifying variants. Clinical follow up was collected for 15/18 patients diagnosed before 2012 (median 48 mo, range 8 to 108 mo). All patients with typical OFMT and two patients with atypical OFMT were alive and free of disease. Recurrence occurred in both patients with malignant OFMT, and one patient developed metastases to the lungs. No deaths were recorded.
Conclusions: These results further support criteria for the diagnosis of malignant OFMT. Dermatopathologists should be aware of this unusual tumor given its superficial presentation and potential for aggressive behavior. Careful attention to the morphologic features should allow an accurate diagnosis in most cases.
Category: Dermatopathology

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 68, Wednesday Morning


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