Radiation Forms of radiation that cause cancer include ultraviolet (UV) radiation and
radon. UV radiation is part of sunlight. It is the leading cause of skin cancer. Radon
is a natural radioactive gas that seeps into buildings from the ground. It can cause
lung cancer (Figure21.11).
Figure 21.11: The mutations that cause cancer may occur when people are exposed to
pathogens, chemicals, or radiation. Some common causes of cancer are shown here. ( 9 )
Sometimes cancer cells break away from a tumor. If they enter the bloodstream, they are
carried throughout the body. Then, the cells may start growing in other tissues. This is
usually how cancer spreads from one part of the body to another. Once this happens, cancer
is very hard to control.
Common Types of Cancer
Cancer occurs mainly in adults, especially in adults over age 50, as more mutations accu-
mulate in cells over time. The most common type of cancer in adult males is cancer of the
prostate gland. The prostate gland is part of the male reproductive system. Prostate cancer
makes up about one third of all cancers in men. The most common type of cancer in adult
females is breast cancer. It makes up about one third of all cancers in women. In both men
and women, lung cancer is the second most common type of cancer. Most cases of lung
cancer occur in smokers.
Cancer can also occur in children. However, childhood cancer is rare. Leukemia is the main
type of cancer in children. It makes up about one third of all childhood cancers. It occurs
when the body makes abnormal white blood cells.