Bone cancer. Coloured scanning electron micrograph (SEM) of bone cancer precursor cells on the surface of a bone. They will develop into an osteoclastoma or giant cell tumour, a type of bone cancer that usually affects the ends of the long bones. These cells are monocytes, which circulate in the blood prior to entering tissues where they differentiate into macrophage cells. In time, these will join together into a large, multi- nucleated cell called an osteoclast. Osteoclasts are normally present in bones to absorb and remove unwanted bone tissue during normal bone regeneration but they can become cancerous. Magnification: x3570 when printed 10cm wide.