Cancer

Cancer is not a single disease but a large family of related ones that share the same basic fault: some of the body's own cells escape the controls that tell them when to divide and when to die. These cells accumulate, often forming a lump called a tumor, grow into neighboring tissue and can travel in blood or lymph to start new growths elsewhere, a process called metastasis.

The underlying cause is damage to genes. Mutations can switch on oncogenes, which push cells to divide, or disable tumor suppressor genes and DNA repair genes, which normally act as brakes and repair crews. These changes come from copying errors during cell division, from exposures such as tobacco smoke, ultraviolet light and certain viruses, or occasionally from a parent. Several changes usually have to build up, one reason cancer becomes more common with age.

Cancers are named for the tissue where they start: carcinomas in epithelial linings, sarcomas in bone and soft tissue, leukemias in blood-forming marrow and lymphomas in immune cells. Main treatments are surgery, radiotherapy, chemotherapy, hormone therapy, targeted drugs and immunotherapy.