chondroblastoma
A benign, chondroid-producing, well-circumscribed, lytic neoplasm usually arising from the epiphysis of long bones. It is characterized by the presence of chondroblasts, osteoclast-like giant cells, chondroid formation, calcification, and mitotic activity. In aggressive cases, there is rearrangement of the 8q21 chromosome band. It occurs most frequently in children and young adults and rarely metastasizes.