This depends largely on the organ of the body where cells first grow abnormally. Doctors customarily consider tumors originating from different organs as different diseases because of the variation in the causes, symptoms, course of disease and prognosis as well as approach to treatment. Cancer is a very common disease. One in three persons will be diagnosed with cancer some time in their life and it will eventually affect three out of every four families. One in five deaths in the United States is due to cancer.
Cancer develops in people of all ages but most often in the middle-aged and the elderly.
The number of cancer cases has risen dramatically over the past 40 years, but much of this increase is a reflection of the increase in population, especially in the older age groups. Cancers of the prostate, lung and colon are the most common types diagnosed among adult males. Breast, lung and colon cancers are the most common among females. Researchers do not fully understand why some people develop cancer while others do not. Susceptibility to cancer-causing agents probably varies among individuals due to genetic factors.