Definition - What does Cancer mean?
Cancer is the name given to a collection of related diseases, all of which involve some of the body's cells dividing uncontrollably without stopping and spreading into surrounding tissues. Normally cells grow and divide into more cells as the body needs them, and when they are damaged or die, new cells replace them. In the case of cancer, the DNA is damaged and this process descends into disorder.
Safeopedia explains Cancer
Due to the fact that our DNA provides our cells with the instructions we need to maintain healthy cell reproduction, if DNA is damaged in some way due to an inherited genetic disorder, radiation exposure, or exposure to carcinogens, which can affect DNA's structure to the point where genetic mutation occurs, then cancer can form. This can happen anywhere in the body and has many causes. Cancer is divided into categories based on the cells where it originated.