Ossifying Fibromyxoid Tumor: A Review With Emphasis on Recent Molecular Advances and Differential Diagnosis.

CONTEXT.—: Ossifying fibromyxoid tumor (OFMT) is a rare, slow-growing mesenchymal neoplasm of uncertain histogenesis with intermediate malignant potential. OBJECTIVE.—: To highlight the most important diagnostic features, including morphologic, immunohistochemical, and molecular findings; to provide comparisons to other entities in the differential diagnosis; and to provide a summary of the clinical features and outcomes in cases reported to date. DATA SOURCES.—: The data sources include recently published literature encompassing OFMT and tumors in the histologic differential diagnosis, and cases from institutional files. CONCLUSIONS.—: Ossifying fibromyxoid tumor is important to recognize because of its low-grade morphology but potential for recurrence and metastasis. Recent molecular analysis has expanded the morphologic spectrum of OFMT, with additional cases discovered that are enriched for aggressive behavior. The diagnosis can often be rendered through a combination of morphology and coexpression of S100 protein and desmin, although only a minority of cases described contain all of these primary features. In cases that do not have all of these features, a high index of suspicion guided by morphology and exclusion of other tumors in the histologic differential diagnosis can lead to the correct diagnosis. Growing access to molecular genetic testing will become increasingly important for correct diagnosis of tumors at the ends of the morphologic spectrum.