Bone cancer. Light micrograph of a section through bone revealing an osteosarcoma. This is among the most malignant of cancers, and is more common in young people. The cancerous cells have produced many areas of disordered bony filaments (osteoid, pale pink). Osteosarcomas usually start in a long bone, often near the knee. They spread rapidly, usually to the lungs. To prevent spread, removal of part of the affected bone or even amputation of the limb may be required. Magnification unknown.