© 2005-2012 American Society of Clinical Oncology (ASCO). All
rights reserved worldwide. Sarcoma is cancer that develops in
the tissues that support and connect parts of the body,
including bone, fat, muscle, and soft tissue. Cancer begins when
normal cells change and grow uncontrollably, forming a mass
called a tumor. A tumor can be benign (noncancerous) or
malignant (cancerous, meaning it can spread to other parts of
the body). Osteosarcoma is a cancer of the bone that destroys
tissue and weakens the bone. Osteosarcoma starts in immature
bone cells that normally form new bone tissue. Rarely, it can
also occur as a tumor in the soft tissues of the body, outside
the bone. Osteosarcoma most often starts in the bones around the
knee joint, at the lower end of the femur (thigh bone) or the
upper end of the tibia (shin bone). The second most common place
is in the humerus (upper arm bone close to the shoulder).
However, osteosarcoma can develop in any bone in the body.
Osteosarcoma is described as either a medull