Desmoplastic fibroma with malignant transformation.

Desmoplastic fibroma (DF) is a rare neoplasm of bone, showing infiltrative and locally aggressive nature. Here, we report a case of DF with an unusual histology arising in a 41-year-old female in the left distal femur, which was detected by plain x-ray as an osteolytic lesion and by magnetic resonance imaging as a well-demarcated mass with endosteal scalloping. Pathologically, the tumor was composed mainly of bland-looking spindle cells in abundant collagenous stroma, accompanied with areas of myxofibrosarcomatous and malignant fibrous histiocytomatous components. These histologically different areas were admixed with each other. The array-based comparative genomic hybridization study on the histologically different areas showed some specific gained or lost loci according to their histologic features. The specific genetic events and the histologic features of this case might represent the malignant transformation of DF.