MSH: A usually benign tumor composed of cells which arise from chondroblasts or their precursors and which tend to differentiate into cartilage cells. It occurs primarily in the epiphyses of adolescents. It is relatively rare and represents less than 2% of all primary bone tumors. The peak incidence is in the second decade of life; it is about twice as common in males as in females. (From Dorland, 27th ed; Holland et al., Cancer Medicine, 3d ed, p1846),NCI: A benign, lytic neoplasm usually arising from the cartilage in epiphysis and metaphysis of bone. It is a well circumscribed tumor characterized by the presence of chondroblasts, osteoclast-like giant cells, myxoid stroma formation, calcification, and mitotic activity. In aggressive cases, there is rearrangement of the 8q21 chromosome band. The tumor occurs most frequently in children and young adults.