Preventing Cancer

Cancer Progress Report 2016: Contents

In this section you will learn:

  • More than half of global cancer cases are a result of preventable causes.

  • Not using tobacco is the single best way a person can prevent cancer from developing.

  • About 20 percent of U.S. cancer diagnoses are related to people being overweight or obese, being physically inactive, and/or consuming a poor diet.

  • Many cases of skin cancer could be prevented by protecting the skin from ultraviolet radiation from the sun and indoor tanning devices.

  • The number of U.S. cancer cases attributable to human papillomavirus (HPV) infection is rising, but most U.S. adolescents have not received the full HPV vaccine course.

  • Exposure to environmental cancer risk factors remains a challenge for certain segments of the U.S. population.

Factors that increase the chance of developing cancer are referred to as cancer risk factors. These factors directly or indirectly increase the chance that a cell will acquire a genetic mutation and therefore increase the chance that a cell will become cancerous (see sidebar on Why Did I Get This Cancer?). Decades of research have led to the identification of numerous cancer risk factors (see Figure 3) (27).

Many of the risk factors that have the biggest impact on cancer incidence are avoidable (see Figure 3). For example, many cases of cancer could be prevented either by individuals modifying their behaviors or through the development and implementation of new public education and policy initiatives that encourage individuals to avoid cancer risk factors or protect people from cancer risk factors in the workplace or environment. In fact, a recent study suggests that between 40 percent and 60 percent of cancer cases among white Americans could be prevented if each person did not smoke, limited alcohol consumption, maintained a healthy weight, and undertook regular physical activity (29). These lifestyle behaviors also increase risk for cancer in other U.S. racial and ethnic groups, but the absolute contributions of these factors to cancer risk in nonwhite populations remain to be determined.

Many cancer risk factors are also risk factors for other chronic diseases, such as cardiovascular disease, respiratory diseases, and diabetes. Therefore, reducing or eliminating exposure to these factors through behavior modification or public education and policy initiative implementation has the potential to reduce the burden of both cancer and other diseases.

In the United States, many of the greatest reductions in cancer morbidity and mortality have been achieved through the implementation of effective public education and policy initiatives. For example, major public education and policy initiatives to combat cigarette smoking have been credited with preventing almost 800,000 deaths from lung cancer from 1975 to 2000 (31). The researchers concluded, however, that this figure represented just 32 percent of the lung cancer deaths that could have been prevented during that period if tobacco control strategies had completely eliminated cigarette smoking (31).

Clearly, a great deal more research and more resources are needed to understand why some individuals continue to engage in risky behaviors despite current public education and policy initiatives, and how best to help these individuals eliminate or reduce their risk of some cancers. One recent study suggested that the way that public education messages are framed can dramatically influence whether or not an individual modifies his or her behavior because it showed that dieting individuals who saw a message focusing on the negative aspects of unhealthy food actually increased their consumption of unhealthy foods (32).

Eliminate Tobacco Use   

Smoking tobacco exposes a person to toxicants that can cause genetic mutations, increasing his or her risk of developing not only lung cancer, but also 17 other types of cancer (see Figure 4) (33). It is responsible for one in every three cases of cancer diagnosed in the United States each year (27). Therefore, one of the most effective ways a person can lower his or her risk of developing cancer, as well as other smoking-related conditions such as cardiovascular, metabolic, and lung diseases, is to avoid or eliminate tobacco use.

Since the relationship between tobacco use and cancer was first brought to the public’s attention in 1964 (37), the development and implementation of major public education and policy initiatives have driven down cigarette smoking rates among U.S. adults from 42 percent in 1965 to 15 percent in 2015 (20, 34). In addition, the most recent data show declining use of cigarettes among high school students: In 2011, 15.8 percent of high school students were current users of cigarettes, compared with 9.3 percent in 2015 (38).

We have made tremendous progress reducing the public health burden of tobacco use, with researchers estimating that more than 8 million smoking-related deaths were prevented in the United States from 1964 to 2014 as a result of declines in cigarette smoking rates (39). The reductions in cigarette smoking rates have not been evenly distributed among all segments of the population, as defined by race, ethnicity, educational level, socioeconomic status, and place of residence (40). For example, 29.2 percent of non- Hispanic American Indians/Alaska Natives, 18.2 percent of non-Hispanic whites, 17.5 percent of non-Hispanic blacks, 11.2 percent of Hispanics, and 9.8 percent of non- Hispanic Asians are smokers (40).

In addition, U.S. adult use of other tobacco products that can cause certain types of cancer—cigars, smokeless tobacco products (e.g., chewing tobacco and snuff), and pipe tobacco—has not changed over the past decade (41). Moreover, use of emerging tobacco products, such as electronic cigarettes (e-cigarettes) and waterpipes, among high school students is increasing rapidly. In 2011, 1.5 percent of high school students were current users of e-cigarettes, and 4.1 percent were current users of hookahs, compared with 16.0 percent and 7.2 percent, respectively, in 2015 (38).

Given that tobacco use and addiction mostly begin during youth and young adulthood, more research into the health consequences of using e-cigarettes and water pipes is urgently needed (43). In particular, we need to fully understand whether e-cigarettes have value as cigarette- smoking cessation aids and how they affect use of other tobacco products by smokers and nonsmokers (see sidebar on E-cigarettes: What We Know and What We Need to Know) (44). We also need more research into the health consequences of smoking marijuana; for example, there is concern it could cause cancer because it involves the burning of an organic material, much like tobacco smoking. The need for this research is driven by the growing number of states that have legalized marijuana use formedical and/or recreational purposes (see Figure 5).

A number of new tobacco control policy initiatives have been recently announced in the United States, the most prominent of which is the decision by the FDA to extend its regulatory oversight to all tobacco products, including e-cigarettes, cigars, pipe tobacco, and hookah tobacco (see sidebar on Enhancing Tobacco Control Through FDA Regulation). In addition, a growing number of cities, counties, and states, most recently California, have passed legislation raising the minimum age of sale of tobacco products to 21 (47). This is important because nearly everyone who buys cigarettes for U.S. minors is under the age of 21 (47), and it has been predicted that if implemented nationwide, such legislation could lead to a 12 percent reduction in smoking prevalence (48).

Maintain a Healthy Weight, Eat a Healthy Diet, and Stay Active

Researchers estimate that one in every five new cases of cancer diagnosed in the United States is related to people being overweight or obese, being inactive, and/or eating a poor diet (49). Therefore, maintaining a healthy weight, being physically active, and consuming a balanced diet are effective ways a person can lower his or her risk of developing or dying from cancer (see sidebar on Reduce Your Risk for Cancer Linked to Being Overweight or Obese, Being Inactive, and/or Consuming a Poor Diet).

Being overweight or obese as an adult increases a person’s risk for 14 types of cancer (see Figure 6) (50), and it is estimated to have been responsible for about 481,000 of the new cases of adult cancer diagnosed worldwide in 2012 (51). Therefore, it is extremely concerning that in the United States, 71 percent of adults age 20 or over are overweight or obese (52), 32 percent of youth ages 2 to 19 are overweight or obese (52), and more than half of U.S. adults and 73 percent of high school students do not meet the relevant recommended guidelines for aerobic physical activity (see sidebar on Physical Activity Guidelines) (20,  53).

Several steps to promote physical activity for all segments of the U.S. population are outlined in Step it up! The Surgeon General’s Call to Action to Promote Walking and Walkable Communities and in the U.S. National Physical Activity Plan (57, 58). Nevertheless, concerted efforts by individuals, families, communities, schools, workplaces, institutions, health care professionals, media, industry, government, and multinational bodies are required to implement any strategy to promote the maintenance of a healthy weight and the participation in regular physical activity.

In addition, intensive efforts by all stakeholders are needed if we are to increase the number of people who consume a balanced diet, such as that recommended by the U.S. Department of Health and Human Services and the U.S. Department of Agriculture in the 2015—2020 Dietary Guidelines for Americans (59). One recent policy initiative to help people make better informed food choices and meet the new dietary guidelines is the FDA decision to change the regulatory requirements for the information that manufacturers must provide on nutrition facts labels on food packaging, including the new requirement for information about how much sugar has been added to the food product (60).

The new public education and policy initiatives are important steps toward reducing the burden of cancer caused by being overweight or obese, being inactive, and/ or eating a poor diet. More research is needed, however, to better understand the effect on cancer risk of exposure to these cancer risk factors at various stages of life. For example, recent data suggest that increased body weight during childhood and adolescence may increase risk for colorectal cancer later in life (62, 63), while eating plenty of fruit during adolescence may decrease risk for breast cancer in later life (64), although more research is required to confirm these findings.

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Protect Skin from UV Exposure

For most of the nearly 5 million patients with skin cancer who are treated each year in the United States, their disease was caused by genetic mutations arising as a result of exposure to ultraviolet (UV) light from the sun, sunlamps, tanning beds, and tanning booths (65). In fact, it is estimated that exposure to UV radiation, primarily from the sun, causes as many as 90 percent of U.S. cases of melanoma, the most deadly form of skin cancer. About 8 percent of cases are attributable to indoor tanning (66). Thus, one of the most effective ways a person can reduce his or her risk of skin cancer is by practicing sun-safe habits and not using UV indoor tanning devices (see sidebar on Ways to Protect Your Skin).

Despite the knowledge that the three main types of skin cancer—basal cell carcinoma, squamous cell carcinoma, and melanoma—can be prevented, fewer than 15 percent of men and 30 percent of women use sunscreen regularly on their faces and other exposed skin when outside for more than 1 hour (67), and one in three adults in the United States reports experiencing at least one sunburn in the past 12 months (68). In addition, 6 percent of U.S. adults report using an indoor UV tanning device at least once in the past 12 months (69). The most recent data show that use of indoor UV tanning devices has declined among high school students, from 13 percent in 2013 to 7 percent in 2015, although more needs to be done to reduce this number even further (53, 70).

Continued exposures to UV radiation have fueled a rise in melanoma incidence rates over the past 3 decades (3), and researchers anticipate that the number of new U.S. melanoma cases diagnosed each year will rise dramatically in the coming decades if current trends continue, increasing from 65,647 in 2011 to 112,000 in 2030 (71). Thus, it is vital that individuals, families, communities, schools, workplaces, institutions, healthcare professionals,

media, industry, government, and multinational bodies work together to develop and implement more effective policy changes and public education campaigns to reduce exposure to UV radiation. One policy change currently being considered by the FDA is a ban on the use of indoor UV tanning devices by individuals younger than age 18 (see sidebar on Indoor Tanning Legislation). This measure could be particularly effective at reducing exposure to UV radiation given that recent research showed that placing age restrictions on the use of indoor UV tanning devices reduces the use of these devices by female high school students (72).

Prevent Infection with Cancer-Causing Pathogens

Persistent infection with a number of pathogens—bacteria, viruses, and parasites that cause disease—increases a person’s risk for several types of cancer (see Table 4) (74- 76). It is estimated to have been responsible for about 2 million of the 12.7 million new cases of cancer diagnosed
worldwide in 2008, with more than 90 percent of these cases attributable to just four pathogens: Helicobacter pylori, hepatitis B virus (HBV), hepatitis C virus (HCV), and human papillomavirus (HPV) (76). Therefore, individuals can significantly lower their risk for certain types of cancer by protecting themselves from infection with cancer-associated pathogens or by obtaining treatment, if available, to eliminate an infection (see sidebar on Preventing or Eliminating Infection With the Four Main Cancer-causing Pathogens).

Although there are strategies available to eliminate, treat, or prevent infection with Helicobacter pylori, HBV, HCV, and HPV, it is clear that these strategies are not being used optimally. For example, even though the CDC recommends screening all U.S. adults born from 1945 to 1965 for HCV infection and there are several therapeutics that can eliminate HCV infection, it is estimated that there are at least 3.5 million people in the United States currently infected with HCV (79). Given that infection with HCV is estimated to be responsible for 22 percent of cases of hepatocellular carcinoma (HCC)—the most common form of liver cancer—in U.S. adults age 68 or older (80), the burden of HCC could be significantly reduced through more effective implementation of HCV screening and treatment.

In addition, the development of strategies to increase uptake of the three FDA-approved HPV vaccines could have an immense impact on cancer prevention (see sidebar on How Do the Three FDA-approved HPV Vaccines Differ?). It is estimated that in the United States, more than 53,000 cases of cervical cancer and thousands of cases of other HPV-related cancers, including many anal, genital, and oral cancers, could be prevented if 80 percent of those for whom HPV vaccination is recommended—girls and boys at age 11 or 12—were to be vaccinated (81). However, the most recent estimates from the CDC show that in 2014, only 40 percent of girls ages 13 to 17 and 24 percent of boys of the same age had received the full course of three or more doses of an HPV vaccine (82). This low coverage stands in stark contrast to three-dose HPV vaccine coverage in other countries (81, 83) (see Figure 7).

Several steps to address the low HPV vaccine coverage in the United States were recently recommended by the National Vaccine Advisory Committee (NVAC), a federal advisory committee that provides vaccine and immunization policy recommendations to the U.S. Department of Health and Human Services (85). Among the objectives outlined by the NVAC was the development of comprehensive communication strategies for physicians to encourage HPV vaccination at every opportunity. The need for these strategies is highlighted by recent data showing that many physicians recommend HPV vaccination inconsistently, behind schedule, or without urgency (86).

Limit Exposures to Environmental Risk Factors

There are many other cancer risk factors in our environment, including environmental pollutants and occupational cancer-causing agents (87) (see Figure 3). It can be difficult for people to avoid or reduce their exposure to many of these factors. Therefore, it is imperative that policies are put in place to ensure that everyone lives and works in a safe and healthy environment.

In the United States, some policies that help protect people from known cancer risk factors have been in place for several decades. For example, there are numerous policies to help prevent exposure to asbestos, which can cause mesothelioma, an aggressive type of cancer for which there remain few treatment options (88). There are also guidelines for reducing exposure to radon gas, which is released from rocks, soil, and building materials and is the second most common cause of lung cancer in the United States after cigarette smoking (89). That said, compliance with these guidelines is not mandatory. It is estimated that about one in every 15 U.S. homes has radon levels at or above 4 picocuries per liter of air, which is the level at which the U.S. Environmental Protection Agency (EPA) recommends taking action (89).

As we learn more about environmental and occupational cancer risk factors and identify segments of the U.S. population exposed to these, we need to develop and implement new and/or more effective policies. We also need to do more worldwide to limit exposure to well- established environmental and occupational cancer risk factors such as asbestos.

One environmental pollutant that was recently classified by the International Agency for Research on Cancer (IARC), an affiliate of the World Health Organization, as having the ability to cause cancer in humans, is outdoor air pollution (90). Outdoor air pollution is a complex cancer risk factor because it is a mixture of pollutants that vary over space and time as a result of differences in climate and sources of outdoor air pollution. We do know, however, the sources of much outdoor air pollution—emissions from motor vehicles, industrial processes, power generation, and the burning of solid fuels for domestic heating and cooking— and it is clear that new policy efforts to reduce the release of pollutants into the atmosphere are needed if we are to reduce the burden of cancer.

Growing knowledge of the environmental pollutants to which different segments of the U.S. population are exposed highlights new opportunities for education and policy initiatives to improve public health. For example, arsenic exposure is a well-established cause of bladder cancer. A recent study identified drinking water containing low- to-moderate levels of arsenic, obtained from shallow-dug private wells, as a potential contributor to the elevated incidence of bladder cancer that has been documented in New England for more than 5 decades (91).

In other cases, increasing knowledge of the presence of environmental pollutants in certain geographic regions emphasizes the need for more research to inform the future development and implementation of education and policy initiatives. For example, researchers recently found elevated levels of uranium and other heavy metals in abandoned mines in northeastern Arizona and are now investigating how this might affect nearby Native American communities (92).

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Cancer Progress Report 2016 Contents

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