Causes
The exact cause of cancer is not known, but various factors are likely at play. Although genetic factors have been linked to certain types of cancers, less than 10% of cancers are inherited. About 5% of breast cancers are associated with mutated genes known as BRCA1 and BRCA2. These two inherited genes account for about 50% of the inherited forms of breast cancer. Most forms of cancer are due to genetic mutations of cells that occur within a person's life as a result of environmental factors such as cigarette smoke or exposure to radiation. Exposure to the following environmental factors can cause cancer:
- Tobacco smoking: Smoking causes lung cancer; and is also associated with an increased risk for cancers of the mouth (oral cancers), larynx, esophagus, bladder, and cervix.
- Chemicals: Exposure to industrial dyes, asbestos, and benzene is linked to cancer.
- Ionizing radiation: A connection between ionizing radiation and cancer has been made, but the exact amount of radiation exposure that increases the risk of cancer is not known.
- Viruses: Certain viruses, such as the human immunodeficiency virus (HIV, which causes AIDS) are associated with an increased risk of liver cancer, lymphomas, and sarcomas. Other viruses include human papilloma virus (which causes venereal warts) and herpes simplex virus 2 (HSV-2) (which causes genital herpes) - both these viruses are linked to an increased risk of cervical cancer.
- Sunlight: Prolonged exposure (e.g., suntanning) causes skin damage and may result in skin cancer.