Bone cancer cell. Coloured scanning electron micrograph (SEM) of a bone cancer precursor cell. This is a monocyte, a cell that circulates in the blood prior to entering tissues where it develops into a macrophage cell. Several macrophage cells will later join together to form a large, multi- nucleated cell called an osteoclast. Osteoclasts are normally present in bones to absorb and remove unwanted bone during normal bone regeneration, but can become cancerous. They can develop into an osteoclastoma or giant cell tumour, a type of bone cancer that usually affects the ends of the long bones.