Cancer 

Cancer is a class of diseases characterized by out-of-control cell growth. In all types of cancer, some of the body's cells begin to divide without stopping and spread into surrounding tissues. Normally, cells in the body follow an orderly path of growth, division, and death. Programmed cell death is called apoptosis, and when this process breaks down, cancer begins to form. Unlike regular cells, cancer cells do not experience programmatic death and instead continue to grow and divide. These extra cells can form a mass called a tumor.