1) Cancer is a disease where some of the body's own cells repeatedly divide without control as the result of a mutation. The new cells may form a malignant tumor (a neoplasm) or propagate throughout the body.
Cancer has become an important problem with the rise in life expectancy, as the mutations become more likely the longer a person lives. Though great progress in treatment has been made, many cancers reach advanced stages remain incurable and ultimately fatal. Thankfully for patients with incurable cancer, the last 20 years have seen the widespread availability of palliative care.
Cancer is treated by an oncologist, a doctor specialized in the treatment of malignant disease.