Scientists have learned that cancer is caused by changes (called alterations) in genes that control normal cell growth and cell death. Certain lifestyle and environmental factors can change some normal genes into genes that allow the growth of cancer. Many genetic changes that lead to cancer are the result of tobacco use, diet, exposure to ultraviolet (UV) radiation from the sun or exposure to carcinogens (cancer-causing substances) in the workplace and in the environment. Some gene alterations are inherited.
However, having an inherited gene alteration does not mean that the person is certain to develop cancer; it means that the chance of getting cancer is increased. Scientists continue to examine the factors that may increase a person's chance of developing cancer.
Although being infected with certain viruses, such as the human papillomavirus (HPV) and human immunodeficiency virus (HIV), increases the risk of some types of cancer, cancer is not contagious. A person cannot catch cancer from someone who has the disease. Scientists also know that an injury or bruise does not cause cancer.