No one knows for sure why a normal cell becomes a cancer cell. Many causes of cancer have been identified. Scientists agree that people can get cancer through repeated long-term contact with carcinogens . These include tobacco, sunlight, X-rays, and certain chemicals that may be found in the air, water, food, drugs and workplace. Our personal habits and lifestyle may contribute to most cancers.
Cancers develop slowly in people.
They usually appear five to 40 years after exposure to a carcinogen. For example, cancer of the lung may not occur until 30 years after a person starts smoking. This long latency period is one of the reasons it is difficult to determine what causes cancer in humans. Cancer is a very common disease. One in three people will be diagnosed with cancer at some time in their life.