Cancer cell. Computer-enhanced confocal light mic- rograph of a cancer cell with two nuclei (pink). Normal cells have one nucleus, but cancer cells often have two. The structural protein actin (green) forms part of the cell's cytoskeleton, which supports its internal structures. Cancer is a disease caused by the rapid, uncontrolled pro- liferation of abnormal cells, which can invade and damage surrounding tissues. Magnification unknown.