What is Osteosarcoma?

Osteosarcoma is a type of bone cancer that occurs mainly in teenagers and adolescents, but may also affect older adults. Bone cancer develops when cells in the bones begin to grow rapidly and uncontrollably. The human skeletal system is made up of many bones that give support, structure and protection to the body. Bones have a hollow center that is filled with bone marrow, the soft, spongy tissue where blood cells are produced. The hard, outer part of the bone is called the cortex. Bones are connected to other bones by ligaments, which are bands of threadlike, fibrous tissue. Bones also contain cartilage, which is a tough, flexible covering that protects the joints and the ends of bones. There are two main types of cells in the bone: osteoclasts and osteoblasts. Osteoclasts help break down areas of old, weakened bone matrix and osteoblasts help to rebuild these areas by laying down new bone.

Osteosarcomas begin in the osteoblasts, the cells that help rebuild areas of weakened bone. About half of all cases of osteosarcoma involve the knee, but it may also form in the upper arms, pelvis or other bones. Osteosarcoma often forms at the ends of the long bones in the legs and arms, which grow most quickly during teenage growth spurts.