Environmental Oncology 101

Vulnerable Groups

Not everyone who becomes exposed to a toxin or carcinogen will develop a disease; however, certain groups within a given population may be at higher risk for environmentally caused diseases. These vulnerable groups may have increased risk of contracting an environmentally caused disease due to either genetic reasons or their lack of empowerment and ability to change their environments. Vulnerable groups include:

• Poorer people (For example, hazardous waste sites and landfills tend to be located in and around lower-income neighborhoods.)
• Women, especially pregnant women (The developing fetus is especially susceptible to environmental exposures.)
• Children
• Elderly
• Ethnic minorities (Often due to social or economic inequalities and differences in access to health care services, ethnic minorities experience higher rates of certain diseases.)
• People with disabilities or chronic illnesses
• People living in developing countries

Environment and cancer
Sources of carcinogens in the environment include:

• Cigarette smoke – direct and secondhand
• Smokeless tobacco, including chewing tobacco and snuff
• Alcohol
• Radiation
• Air pollution
• Pesticides, herbicides
• Occupational exposures to chemicals
• Prescription hormones, such as hormone-replacement therapy (HRT)
• Many cosmetics
• Many common household products
• Lifestyle factors, including diet and physical activity
• Excessive sunlight exposure
• Certain infectious organisms

For a complete list of substances that have been studied and are known as potential carcinogens, see the National Toxicology Program’s 11th Report on Carcinogens 11th Report on Carcinogens.

The link between the environment and cancer has been known for a long time, yet relatively few substances have been proven as carcinogens. Several reasons exist for this lack of knowledge. Due to the long span of time between an exposure and onset of cancer, scientists have had trouble proving that certain exposures cause particular cancers. In addition, cancer often has multiple causes, which makes proving that one particular substance causes cancer even more complicated. Because a certain type of cancer may look the same in many different people, doctors cannot tell what caused a particular type of cancer to develop. Thus, no proven method to identify environmentally caused cancer exists, even though at least two-thirds of all cancers are thought to have such a cause.

Occupational exposures have been somewhat easier to research, and much of the current knowledge about the environment and cancer comes from studying workers in jobs that have higher-than-normal rates of certain cancers. Job exposure is easier to track, since the use of chemicals often is documented, and these exposures occur in certain groups of people over defined periods of time. Because work activities involving chemicals or other toxins often occur in concentrated or high doses throughout the work day, the overall exposure to a substance may be much greater in certain industrial workers than in the general public. From this information, doctors and scientists more easily can relate certain cancers to specific agents used in the workplace.