Cancer Exposure and Risk (Part 2)
The cause of many cancer types is unknown and likely determined by the combined effects of multiple factors. However, major risk factors for cancer include lifestyle choices such as tobacco use, unhealthy diet, lack of exercise and sun exposure. Genetic factors also appear to play a role in several types of cancer.
Although environmental pollution has been a source of great public concern for decades, there have only been a few well-studied cases of environmental exposures at the community-level. The cancer risks associated with many environmental chemicals are based on studies in the workplace, where exposures are often much greater than they would be in the general public. These earlier studies provide the foundation for building evidence that supports a link between cancers and exposures to environmental pollutants.
Some environmental exposure is potentially avoidable. For example, exposures related to tobacco smoking, can be avoided with behavioral changes. Other environmental factors are less controllable such as carcinogenic compounds released into the ambient air. Furthermore, some risk factors are unavoidable such as age, race or other genetic susceptibilities. It is important to remember that having a risk factor only increases the chances that a person will develop cancer, it does not mean the individual will for sure develop cancer. Also, many people who develop cancer do not have many or any of the currently known risk factors.
Cancer of the Brain and Central Nervous System Exposure and Risk
About 5% of brain tumors are due to hereditary factors. Persons with rare genetic conditions such as Li-Fraumeni cancer family syndrome, tuberous sclerosis, von Recklinghausen's disease (neurofibromatosis type 1), neurofibromatosis type 2, von Hippel-Lindau disease, and familial polyposis are at greater risk for cancer of the brain and other parts of the central nervous system.
Research is being conducted to determine whether additional factors may be linked to cancer of the brain and other parts of the central nervous system, however, much more research is necessary. Other factors that have been investigated include:
- Electromagnetic fields (including cellular and cordless phone use)
- Occupational exposure to asbestos, arsenic, wood dust, benzene, mercury, lead, pesticides, and other chemicals
- Ingestion of n-nitroso compounds through food, drinking water, and smoking
- Use of hair dyes and sprays
- Dietary calcium intake
- Allergies and other immune system factors
- Drinking alcohol
- Genetic polymorphisms
- Family history
- Head trauma
- Reproductive and Hormonal factors
Risk factors are different for children and for adults. Cancerous brain and spinal cord tumors are the second most common types of cancer in children. Little is known about the causes of this group of diseases. Established risk factors include exposure to therapeutic doses of ionizing radiation, rare hereditary syndromes, and family history.
Thyroid Cancer Exposure and Risk
Although a person with thyroid cancer may have a risk factor, the degree to which that risk factor contributes to the cancer may be difficult to determine. A few risk factors that increase the likelihood to develop thyroid cancer have been established. These include:
- Gender and Age
- Diet Low in Iodine
- Hereditary Conditions
Non-Hodgkin Lymphoma Exposure and Risk
Most patients with non-Hodgkin lymphoma have no known risk factors; however, a few risk factors that may make a person more likely to get non-Hodgkin lymphoma have been determined. These factors include:
- Treatment with Chemotherapy Drugs
- Radiation Exposure
- Weakened Immune Systems
- Autoimmune Diseases
- Certain Infections
- Body Weight and Diet
Leukemia Exposure and Risk
As with most cancers, the cause of most leukemias is unknown. Generally, some risk factors include:
- High doses of ionizing radiation
- Genetic abnormalities, including Downs syndrome
- Rare viruses
- Long-term benzene exposure
- Chemotherapy drugs known as alkylating agents
The relationship of these factors may depend on the type of leukemia. Moreover, adult leukemia risk factors differ from those of children. For adult-onset leukemia, the most firmly established environmental risk factor is exposure to ionizing radiation; benzene, agricultural exposures, and smoking also have been linked to elevated risk. For acute lymphocytic leukemia in children, their exposure to ionizing radiation and a parent's exposure to pesticides and other chemicals may increase risk.