Cancer is a widespread disease that affects a large majority of the population either directly, because they develop it, or indirectly, because they know or are related to someone with the disease. Cancer can form in almost any organ or area of the body and while the disease is widespread, it is hard to treat. Some treatment does exist but a true "cure" for cancer is still many years away. In spite of our lack of knowledge of many of the exact details of cancer, there is a great deal that is understood about its overall behavior. In the simplest terms, Cancer is what happens when some cells in the body undergo a mutation, which damages their DNA, and results in a cell that does not undergo cell death, called apoptosis, ignoring the normal cell cycle. This mutated cell refuses to die and multiplies significantly, with lethal consequences for the body. There are two major differences between a cancerous cell and a normal cell, these are: the cancer's uncontrolled growth, and the resistance of cancer to cellular death. The uncontrolled growth of cancer cells causes even one cancerous cell to rapidly grow to form a full-fledged tumor, which causes damage to surrounding tissue as it grows in size and spreads throughout the body.
In order to understand the source of these special properties of cancer cells, it is important to understand the way Genes and Proteins interact, the role of proteins in the cell, and how genes and proteins influence the Cell Cycle and Mitosis, the normal steps a cell goes through as it grows and divides when it is non-cancerous.