Bone cancer cells. Coloured scanning electron micrograph of osteosarcoma cancer cells. Osteosarcoma is an aggressive malignant neoplasm arising from primitive transformed mesenchymal cells. It is the most common histological form of primary bone cancer. Most people diagnosed with osteosarcoma are under the age of 25, and it is thought to occur more often in males than females. Osteosarcoma is often treated with a combination of therapies that can include surgery, chemotherapy and radiation therapy. Magnification: x1000 when printed at 10 centimetres wide.