Cancer is described as the condition wherein the old cells of the body do not die. What happens is that they become abnormal. They start to grow, divide, and spread. The extra cells that start to grow will start to form a tumor. The problem with cancer cells is that they are not detected by the body as abnormal so they are not targeted by the immune system.
Malignant tumors have the tendency to grow and spread at a very fast rate. The immune system alone will not be enough to fight the abnormal cells but if the condition would be detected early, there are more treatments that are available.
Cancer is a kind of condition wherein it would cause abnormal cells to grow in a rapid manner. The cell growth is so rapid that it would form tumors or masses. The old cells that are supposed to die, do not die. The time would come when these cells would take over the normal, healthy cells. In the process, the whole body deteriorates because the cancer cells are not supposed to take over.
The treatments for Cancer are meant to stop the growth of abnormal cells and banish them from the body. This can just happen rapidly. All it takes is one cell to start behaving abnormally for it to multiply rapidly while the normal cells die.