Cancer describes any of a group of diseases which are characterized by the uncontrolled growth of cells that are destructive to tissues and organs in the body, and can lead to death. Cancer cells form when normal cells become damaged and then multiply. It is not uncommon for a cell to form abnormally or become damaged, but in most cases the cell simply self-destructs in a process called apoptosis. Malignant cells appear to the body’s immune system to be normal cells, therefore the body’s defenses will not attack them.
Most cancer cells multiply and stay localized, at least at first, forming a tumor, with one notable exception to this rule being leukemia. Not all tumors are cancerous, however. Benign tumors are growths that can share certain characteristics with cancerous tumors, but are self-limiting and non-destructive. They mostly do not come back after they are removed.
Malignant or cancerous tumors form as a result of a mutation or other damage to the genetic material of a normal cell. This occurrence itself happens often in the body, but it almost always stopped as the damaged cell kills itself, stopping the mutation from spreading. Strategic cell death or apoptosis is essential to the growth and survival of all living things. This fact becomes especially evident when apoptosis fails to occur. The mutated cell survives to duplicate, and then these two cells divide, forming more.
Other mutations can occur, and replication continues unchecked, until a tumor is formed. The normal process of cell division is not like the growth of malignant cells, which is unmitigated by apoptosis. These cancer cells are somehow not recognized as harmful by the body’s natural defense systems and are allowed to continue multiplying. If not removed, this group of cells can begin to destroy the tissue in which they formed, as well as invading other areas of the body.
Cancer treatments are mostly focused on removing and destroying the malignant cells themselves. They can range from surgery to remove tumors, to drugs which try to choke off the tumor’s blood supply, to radiation therapy. Surgery is usually the preferred method of removing localized tumors, and it is necessary to also remove a small margin of healthy tissue, since even one microscopic cancer cell can regrow into a tumor. Little is known about the reasons why mutated cells become cancerous, but there is a great deal of research being done with the goal of preventing and more efficiently treating all types of cancer.