Cancer and the Environment
Exposures to natural and man-made substances in the environment (environmental factors) are estimated to play a role for at least two-thirds of all the cases of cancer in the United States. These environmental factors can include lifestyle choices including: cigarette smoking, alcohol consumption, diet, exercise, and exposure to certain medical drugs and hormones; and environmental exposure to radiation, viruses, bacteria, and chemicals that may be present in the air, water, food, and the workplace.
Female Breast Cancer and the Environment
Breast cancer is the most commonly diagnosed cancer in women in the United States. Breast cancer will develop in approximately one in eight women during their lifetimes. The incidence of this disease is decreasing, primarily among women older than 50 years. The disease usually occurs in women but men can have breast cancer too.
Only about 47% of breast cancers that occur in the United States can be attributed to established risk factors. While animal studies indicate that environmental contaminants can cause breast tumors, clear links between environmental exposures (other than ionizing radiation) and human breast cancer have not been established.
Exposure to chemicals such as poly aromatic hydrocarbons (PAH), benzene, and organic solvents and passive smoking have been suspect in causing breast cancer, but the evidence is weak and more research is needed.
Lung Cancer and the Environment
Lung cancer is the leading cause of cancer deaths in the United States. Lung cancer forms in the tissue of the lung, usually in the cells lining the air passages. Cigarette smoking is the single most important risk factor for, and leading cause of, lung cancer. Exposure to radon is the second leading cause of lung cancer.
Occupational substances categorized by the International Agency for Research on Cancer (IARC) as known lung carcinogens include:
- Bischloromethyl ether
- Polycyclic aromatic compounds
- Vinyl chloride.
Environmental tobacco smoke (ETS) is a recognized causal factor for lung cancer and air pollution may increase lung-cancer risk slightly. The impact of outdoor air pollution on lung cancer needs further study.
Bladder Cancer and the Environment
Bladder cancer is more common among older persons, more common among men, and occurs more frequently in white persons.
Reoccurrence of bladder cancer is common; consequently, the prevalence of bladder cancer is high. Incidence rates of bladder cancer vary geographically with higher rates in the northeastern United States. Known risk factors such as smoking and occupational exposures do not explain the geographic variations.
The relationship between bladder cancer and drinking water contamination has been researched extensively. High levels of arsenic in drinking water have been well-established as causing cancer; high levels of trihalomethanes, or disinfection byproducts, have also been labeled as probable human carcinogens.
Cancer of the Brain and Central Nervous System and the Environment
The American Cancer Society (ACS) reports that cancers of the brain or spinal cord account for about 1.3% of all cancers and 2.2% of all cancer-related deaths among adults and children. Cancers of the brain occur in people of all ages but more frequently in two age groups:
- Children aged younger than 15 years
- Adults aged 65 years and older
Cancers of the brain and other parts of the central nervous system are more common in white persons. Cancers of the meninges, part of the central nervous system, are more common in women.
Little is known about the causes of childhood and adult cancers of the brain and other parts of the central nervous system. Several studies of environmental risk factors have presented inconsistent and inconclusive results.
Thyroid Cancer and the Environment
Thyroid cancer has a lower fatality rate than most cancers. Thyroid cancer is much more likely to occur in women and people between the ages of 20 and 55.
The excessive risk for thyroid cancer associated with exposure to external ionizing radiation has been well-established. No other environmental chemicals or physical agents have been associated with this cancer. Other risk factors for this cancer include:
- Dietary factors, especially iodine intake
- Hormonal and reproductive factors
- Benign thyroid nodules and goiter
- Hereditary conditions
- Gender and age
Non-Hodgkin Lymphoma and the Environment
Non-Hodgkin lymphomas are a group of cancers that start in lymphoid tissue, also called lymph or lymphatic tissue. The causes of non-Hodgkin lymphoma are mostly unknown. Specific viruses, immune deficiency, and specific autoimmune conditions have been implicated in increased risk. However, some environmental issues, including exposures to pesticides and solvents, are also being investigated.
Leukemia and the Environment
Leukemia is cancer of the blood cells. When leukemia develops, the body makes many abnormal blood cells.
Leukemia comprises a group of diseases that includes four major types:
- Acute myeloid
- Chronic myeloid
- Chronic lymphocytic leukemia (primarily adult diseases)
- Acute lymphocytic leukemia (a childhood disease).
Sometimes considered a children's disease, leukemia most commonly occurs in adults older than 65 years. Additional research is needed to better understand the relationship between leukemias and the environment. Exposure to high levels of ionizing radiation has been linked to specific types of leukemia in both adults and children.