Which of the following is TRUE about parosteal osteosarcoma?

Parosteal and periosteal osteosarcoma arises from the surface of the bone (juxtacoical) in contrast to the classic osteosarcoma which arises within the bone. Parosteal Osteosarcoma: Parosteal osteosarcoma is a distinct variant of conventional osteosarcoma that accounts for 4% of all osteosarcomas. It arises from the coex of the bone and according to study done by Jelinek et al, intramedullary extensions may seen in few cases especially with high grade tumors. generally it involves the older individual and slight female preponderance is seen. The distal posterior femur is involved in 72% of cases, the proximal humerus and proximal tibia are the next most common frequent sites. The natural history of parosteal osteosarcoma is progressive enlargement and late metastasis. It present as a mass and occasionally is associated with pain. In contrast to classic osteosarcoma, duration of symptoms varies from months to year and generally has better prognosis than classic osteosarcoma with overall survival rate of 75% to 85%. Remember: Tumor size, location and duration of symptoms did not correlate with survival in parosteal osteosarcoma. Ref: Devita 7/e, Page 167