Benign looking giant cell component in dedifferentiated chondrosarcoma: benign or malignant? A case report.

Dedifferentiated chondrosarcomas (DDCS) account for approximately 10% of all chondrosarcoma cases and its 5-year survival is only 10%. The dedifferentiated components of DDCS could be osteosarcoma, malignant fibrous histiocytoma, and fibrosarcoma. In this article, the authors report a rare case of DDCS in a 19-year-old female, in which the dedifferentiated component showed a close histological resemblance to a giant cell tumor of bone. Radiological diagnosis revealed an expansive osteolytic lesion in the epiphysis of right proximal humerus, which also extended to the diaphysis with irregular calcification and focal cortical breakthrough. The biopsy tissue contained the features of a giant cell tumor of bone and well-differentiated cartilage. Pathological examination revealed a biphasic tumor comprising of low-grade chondrosarcoma and nonchondroid giant cell-rich lesion similar to conventional giant cell tumor of bone, and there is an abrupt transition between the 2 components.