Cancer causes: In most individual cases of cancer, the exact cause of cancer is unknown. The causes may include increased genetic susceptibility; environmental insults, such as chemical exposure or smoking cigarettes; lifestyle factors, including diet; damage caused by infectious disease; and many more.

Although they are not causes per se, many characteristics can influence the development of cancer. These include gender, race, age, and the health of the patient's immune system. When common causes for a type of cancer are discovered, this information can be very helpful in prevention and sometimes in treatment.

For example, the link between overexposure to the sun and skin cancer is well-known, and individuals can easily reduce their risk by avoiding suntanning and sunburns. Skin cancer is the most common type of cancer for both men and women.

The second most common cancer in men is prostate cancer, in women it is breast cancer. Lung cancer is the leading cause of death from cancer for both men and women in the U.S.

Cancer is NOT contagious.