Dedifferentiated Chondrosarcoma with Giant Cell-rich Sarcomatous Component Resembling Giant Cell Tumor: A Case Report

ABSTRACT

Dedifferentiated chondrosarcoma is an uncommon bone tumor, defined as a tumor in which two components -a low-grade chondrosarcoma and a high-grade non-cartilaginous sarcoma-coexist with abrupt interface. We report a rare case of giant-cell rich dedifferentiated chondrosarcoma occurred in the right distal femur shaft of a 60 year-old female. The plain X-ray film showed an irregular radiolucent mass. The T2-weighted MRI revealed a heterogeneous high signal intensity. It was an irregular mass composed of bluish-white, translucent chondroid elements and yellowish solid components with extraosseous invasion. Microscopically, a low-grade chondrosarcoma and a giant-cell rich spindle cell sarcoma with areas resembling giant cell tumor were recognized with abrupt transition. Immunohistochemical staining revealed a S100 protein positivity in chondroid cells and a few spindle cells. CD68 was strongly positive in giant cells. Vimentin was positive in both components and smooth muscle actin was positive in some spindle cells. There was no cytokeratin, desmin and myogenin immunopositivity. It is important to be aware of this rare variant of dedifferentiated chondrosarcoma to avoid the misdiagnosis of more common bone tumors including giant cell tumors.