more likely to occur in people who are infected with HIV, which is the virus that causes AIDS (221). This higher risk is attributable to HIV infection, which weakens the immune system. Prior to highly active antiretroviral therapy (HAART) in 1996, people infected with HIV had a 2,800-fold higher risk of Kaposi sarcoma compared to the general population (222). Since HAART, there has been a steady decline in incidence of Kaposi sarcoma; however, rates remain 800-fold higher than in the general population (223). As the population living with HIV continues to age, the burden of cancers, particularly non-AIDS-defining cancers (such as anal, liver, and lung cancers) will continue to rise (224). One study reported that incidence of lung cancer in people with HIV age 60 years and older is higher than the two most common AIDSdefining cancers, NHL and Kaposi sarcoma (225). Limit Exposure to Environmental Risk Factors Environmental pollutants are encountered in the air, drinking water, and food making them nearly impossible to avoid. Federal agencies, including the Environmental Protection Agency and Department of Health and Human Services, set guidelines for the acceptable exposure limits allowed in the environment. However, some individuals experience higher levels of exposure to certain pollutants due to their occupation, living conditions, or daily activities. Exposure to higher than acceptable levels of certain pollutants, without appropriate protection, can increase the risk of certain diseases. Environmental carcinogens, which are substances that can lead to cancer and are present in the environment, include arsenic, asbestos, radon, lead, radiation, and other chemical pollutants. The International Agency for Research on Cancer (IARC) and the U.S. National Toxicology Program (NTP) are both responsible for evaluating substances and exposures and classifying them as carcinogens at the global and national level, respectively. Higher than normal levels of exposure to carcinogens have led IARC to classify certain occupations, such as firefighting and painting, and work environments, such as iron and steel foundries or working around welding fumes, as class 1 carcinogens, meaning they are cancer-causing to humans (see Sidebar 17, p. 52). It can be difficult for some segments of the U.S. population to avoid or reduce their exposure to environmental carcinogens. For instance, racial or ethnic minorities and people living in poverty are often at increased risk of being exposed to high levels of air pollution, which the IARC has designated as a potential cause of cancer in humans. One type of air pollution termed particle pollution refers to a mix of tiny solid and liquid particles that are in the air we breathe. Nearly 36 percent of the U.S. population, representing 119.6 million people, live in places with unhealthy levels of particle pollution (236). New laws, regulations, and policies to reduce the release of pollutants into the atmosphere are necessary to minimize the long-term, adverse health effects of air pollution, including cancer. Other exposures including chronic stress, lack of sleep, and night-shift work have also been shown to increase a person’s risk of developing certain types of cancer (237). The CDC reports that about 11 million adults in the U.S. frequently work night shifts, with certain groups such as men, and Black and non-Hispanic individuals, more likely to do this type of work. In one recent study, researchers found that women age 50 or older who had both day and night shifts were twice as likely to develop breast cancer compared to those who only worked day shifts (238). Although the underlying mechanisms are not clear, researchers believe that disruption of the body’s circadian rhythm (i.e., the internal clock) can alter biological processes that normally help prevent cancer development. Emerging research indicates that avoiding lighting that disrupts circadian rhythms, for example, lighting that is low in blue light may help reduce cancer risk (239-241). Long-term research is needed to understand how exposure to certain light sources, particularly at night, may contribute to cancer risk. As we learn more about environmental and occupational cancer risk factors and identify those segments of the U.S. population who are exposed to these factors, new and equitable policies need to be developed and implemented to reduce cancer risk and improve the health of all populations. Studies have shown that first responders who were involved in the rescue and recovery efforts of the 9/11 terrorist attacks in New York City have increased incidence of melanoma, prostate cancer, thyroid cancer, and tonsil cancer (228). This may be due to higher levels of precancerous mutations in their blood cells when compared to first responders who did not participate in these efforts (229). In 2023, 63.7 million people living in the United States were exposed to daily, unhealthy spikes in particle pollution (236). Reducing the Risk of Cancer Development AACR Cancer Progress Report 2023 51
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