Preventing Cancer: Understanding Risk Factors
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.
There are disparities in the burden of cancer attributable to preventable causes among certain segments of the U.S. population.
Factors that increase the chance of developing cancer are referred to as cancer risk factors. These factors can alter the genetic or epigenetic information in our cells, which may directly lead to cancer development or increase an individual’s chance of developing cancer later in life. Many of the factors that increase a person’s risk of developing cancer, such as smoking, are also associated with worse outcomes after a cancer diagnosis (see Modifying Behaviors to Improve Outcomes).
Decades of basic, epidemiologic, and clinical research have led to the identification of numerous cancer risk factors (see Figure 4). As a result of this work, we know that more than half of all global cancer cases are attributable to preventable causes, including tobacco use, poor diet, physical inactivity, and obesity (20, 31). In addition, vaccination against infection with the human papillomavirus (HPV) and decreasing exposure to ultraviolet (UV) radiation from the sun and indoor tanning devices can further reduce the burden of certain types of cancer (31). Ongoing research may uncover additional cancer risk factors; one area of intensive research investigation is understanding how early life experiences may contribute to cancer development in adulthood (32).
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, such initiatives drove down cigarette smoking rates among U.S. adults by greater that twofold from 1965 to 2015 (34). However, even today, every three out of 10 cancer deaths are caused by cigarette smoking, and lung cancer is still the leading cause of cancer-related deaths for both men and women (35). Thus, it is imperative that we identify strategies to enhance the dissemination and implementation of our current knowledge of cancer prevention. We also need to develop, disseminate, and implement more effective evidence-based practices that reduce risky behaviors in all population groups.
Eliminate Tobacco Use
Tobacco use is the leading preventable cause of cancer and cancer-related deaths. This is because use of tobacco, or exposure to secondhand smoke, exposes people to many harmful chemicals, including more than 60 different chemicals called carcinogens that can cause cancer by damaging DNA, increasing the chances that it will acquire a mutation (35).
Smoking is linked to 17 different types of cancers in addition to lung cancers, and in 2017, it is estimated that it will cause about 190,500 cancer deaths (see Figure 5) (37, 38). Even individuals who smoke fewer than one cigarette per day over their lifetime have higher risk of death than nonsmokers and cessation at any age can reduce the risk of cancer occurrence and cancer-related death (34, 39). 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, development and implementation of major public education and policy initiatives have significantly lowered cigarette smoking rates among U.S. adults. In fact, it is estimated that from 2000 to 2015, total cigarette consumption decreased by over 38 percent (41). During the same period, use of several tobacco products among high school students also declined sharply: In 1999, more than 40 percent of high school students reported being current users of cigarettes, cigars, or smokeless tobacco compared with just 18 percent in 2015 (42).
We have made major strides in reducing the public health burden due to smoking. Researchers estimate that more than 8 million smoking-related deaths were prevented in the United States from 1964 to 2014 because of declines in cigarette smoking rates (44). However, disparities in cigarette smoking rates and smoking-related health outcomes persist among certain segments of the U.S. population. For example, cigarette smoking rates are much higher among individuals with serious mental health and substance-abuse issues (19, 31). In addition, smoking-related cancer deaths vary across states, with the highest rates being in southern states, where up to 40 percent of cancer deaths in men are caused by smoking (45). These estimates are vital for developing and implementing effective tobacco control and cessation programs.
The use of tobacco products other than cigarettes can also cause cancer. Use of such products, which include cigars, smokeless tobacco products (e.g., chewing tobacco and snuff), and pipe tobacco, increased from 2000 to 2015 (38). Electronic cigarettes (e-cigarettes) are a rapidly emerging tobacco product that expose users to a number of harmful chemicals that are known to have adverse health effects. Given that currently we have limited understanding of the long-term effects of e-cigarette use, the U.S. Surgeon General has expressed major concerns about the rise in popularity of e-cigarettes among youth and young adults (47) (see sidebar on E-cigarettes: A Report from the U.S. Surgeon General). Encouragingly, although e-cigarette use rose sharply among high school students from 1.5 percent in 2011 to 16 percent in 2015 (48), the most recent data show a decline in usage to 11.3 percent in 2016 (49).
Since 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 (50). 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 (51).
Even though smoking rates among U.S. adults and youths have declined, it is clear that researchers, clinicians, advocates, and policy makers must continue to work together if we are to eradicate one of the biggest threats to public health. One step to achieving this goal 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). Additional strategies, such as further raising taxes on prices and/or adding prominent pictorial warning labels on cigarette packs, also need to be evaluated (38, 52). Moreover, we need to use current tobacco cessation strategies more widely because approaches such as use of nicotine replacement therapy and prescription medication as well as counseling have been shown to be effective in enhancing the chances of long-term abstinence from smoking (38).
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Maintain a Healthy Weight, Eat a Healthy Diet, and Stay Active
Researchers estimate that 20 percent of all cancers diagnosed in the United States, including some of the most deadly types of cancer such as pancreatic cancer, are related to people being overweight or obese, being inactive, and/or eating a poor diet (38). 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). Exactly how obesity increases a person’s risk for cancer is not well understood, but accumulating evidence indicates a critical role for inflammatory immune cells within the fat tissue (53).
Being overweight or obese as an adult increases a person’s risk for 14 different types of cancer (see Figure 6) (55). According to the most recent data available, in 2012, it caused about 481,000 new cases worldwide (56). Therefore, it is extremely concerning that in the United States, an estimated, 37 percent of adults and 17 percent of youth are obese, while the annual medical cost of obesity is almost $150 billion (57). In addition, more than 70 percent of high school students do not meet the relevant recommended guidelines for aerobic activity (see sidebar on Physical Activity Guidelines), and one in four adults age 50 years and older are physically inactive (58-60).
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 (38). Nevertheless, concerted efforts by individuals, families, communities, schools, workplaces, institutions, health care professionals, media, industry, government, and multinational bodies are required to implement effective interventions that promote the maintenance of a healthy weight or encourage behavioral modifications in overweight or obese populations. Furthermore, new approaches to encourage weight loss among overweight or obese individuals need to be evaluated. For example, a recent trial in the United Kingdom reported that a brief, behaviorally informed intervention from physicians led to significant weight loss in patients who were obese (62).
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 (38). 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 (38). Another policy that is aimed at reducing obesity is the recent introduction of taxes on sugar-sweetened beverages, which is a major contributor of caloric intake among U.S. youth and adults, in seven local jurisdictions within the U.S. (38, 63-65). Ongoing research is needed to evaluate the long-term effects of these policies on consumption, obesity, and obesity-related health outcomes.
Unfortunately, the burden of diet-related disease, including diet-related cancer, is disparately higher in low-income communities and studies show that individuals from the lowest income groups rarely receive weight-loss advice from their health care providers (66). The high cost of fresh produce relative to calorie-dense, nutrient-poor foods is also considered a barrier to healthier eating among those in the lowest-income groups. One statewide initiative designed to address this is Double Up Food Bucks (DUFB) in Michigan, which matches Supplemental Nutrition Assistance Program (SNAP) funds spent at farmers’ markets. Uptake of DUFB was initially low, but a brief intervention, explaining the initiative to those eligible, resulted in a fourfold increase in uptake, as well as significant increases in fruit and vegetable consumption in a low-income, racially and ethnically diverse community in Michigan (67).
New public education and policy initiatives, such as DUFB, are important steps toward reducing the burden of cancer caused by being overweight or obese, being inactive, and/or eating a poor diet. More work is needed, however, to better understand the effect of exposure to these risk factors at various stages of life on cancer development. For example, a recent study showed that weight gain of 2.5 kilograms or more during early to middle adulthood (ages 18 to 55) was associated with an increased risk of developing several chronic diseases, including cardiovascular disease, type 2 diabetes, and obesity-related cancers, later in life (68). Although more research is required to confirm these findings, they highlight the importance of maintaining a healthy weight throughout life.
Protect Skin from UV Exposure
Exposure to ultraviolet (UV) radiation from the sun or indoor tanning devices can cause genetic mutations and poses a serious threat for the development of all three main types of skin cancer—basal cell carcinoma, squamous cell carcinoma, and melanoma, which is the most deadly form of skin cancer. 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 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, and one in three adults in the United States reports experiencing at least one sunburn in the past 12 months (30, 69, 70). In addition, 4 percent of U.S. adults report using an indoor UV tanning device at least once in the past 12 months (38).
Over the past few decades, these continued exposures to UV radiation have fueled a steady rise in melanoma incidence in the United States (71). Thus, it is imperative that multicomponent, community-wide public awareness initiatives as well as restrictive regulatory policies are implemented, to break the current trend and bring down melanoma rates. Based on the findings from a successful public education campaign called “SunSmart” in Australia, the country with the highest skin cancer rates, it is estimated that 230,000 U.S. melanoma cases could be averted between 2020 and 2030 through implementation of nationwide comprehensive skin cancer prevention programs (72, 73). Recently, the Australian campaign has gone digital with the introduction of the “SunSmart” app, which is freely available on Android and Apple devices (73). Whether this effort to personalize and increase access to the message enhances the impact of the campaign needs to be evaluated, but if successful, similar initiatives could be implemented in other countries including the United States.
Reducing indoor tanning also has the potential to reduce melanoma incidence and mortality, as well as the economic costs related to skin cancers (71, 74). In this regard, in the United States, the FDA has proposed a policy change to ban the use of indoor UV tanning devices by individuals younger than age 18. It is estimated that if this rule were implemented it could avert 62,000 melanoma cases and $343 million in treatment costs (38).
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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). The most recent estimate is that 15 percent of all new cancer cases diagnosed worldwide in 2012 were attributable to pathogens (76), the most common of which were Helicobacter pylori, human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), and Epstein-Barr virus (EBV) (76). Thus, individuals can significantly lower their risks 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 that can significantly lower an individual’s risks for developing an infection-related cancer, it is important to note that these strategies are not effective at treating infection-related cancers once they develop. It is also clear that these strategies are not being used optimally. For example, even though the U.S. Preventive Services Task Force (USPSTF) recommended one-time HCV testing for baby boomers in 2013, data from a 2015 national survey showed that only 10.5 out of 76.2 million eligible candidates reported getting tested (77). Given that infection with HCV is estimated to be responsible for six out of 10 liver cancer cases diagnosed since 2000, the burden of hepatocellular carcinoma could be significantly reduced through more effective implementation of HCV screening and treatment (38, 78).
In addition, the development of strategies to increase uptake of HPV vaccines could have an immense impact on cancer prevention (see sidebar on Updated HPV Vaccination Recommendations). Research suggests that HPV vaccination could prevent nearly all cases of cervical cancer, as well as many cases of oral and anal cancer, but only 63 percent of girls and less than 50 percent of boys had received at least one dose of HPV vaccine in 2015 (79). This level of uptake is much lower than occurs for other vaccinations received in adolescence (79). Development of comprehensive communications strategies that allow physicians to encourage HPV vaccination with successful implementation are critical to enhance uptake. In this regard, one recent clinical trial showed an increase in HPV vaccine initiation among 11- and 12-year-olds, when health care providers announced that vaccination was due, rather than having a participatory conversation with the family (80).
Limit Exposure to Environmental Risk Factors
There are a number of factors that we may be exposed to in our environment, including environmental pollutants and occupational agents, that can increase a person’s risk of cancer (see Figure 4). For example, radon is a naturally occurring radioactive gas that comes from the breakdown of uranium in soil, rock, and water; it is the second leading cause of lung cancer in the United States (42). Other examples of environmental cancer risk factors include asbestos, lead, radiation, and benzene. 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.
It is often difficult for people to avoid or reduce their exposure to many environmental cancer risk factors, and not every exposure will inevitably lead to cancer. The intensity and duration of exposure, combined with an individual’s biological characteristics, including genetic makeup, determine the chances of developing cancer over his or her lifetime. Therefore, it is imperative that regulatory policies are put in place to ensure that every person lives and works in a safe and healthy environment.
In the United States, policies that help protect people from some of the known environmental 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, with few treatment options (84). Despite the existence of regulatory policies, the number of deaths from malignant mesothelioma has been increasing in recent years, particularly among younger populations, which underscores the need for greater efforts to prevent exposure (84). Another important element in studying environmental cancer risk factors is to consider the effect of several factors together, since environmental exposures may occur simultaneously. A recent study from the EPA evaluated the environmental quality index (EQI), a measure of overall environmental exposures, and found a potential increase in overall cancer incidence with decreasing environmental quality (85).
It is important to note that there are considerable disparities in the burden of cancer due to exposure to environmental cancer risk factors (30, 38). These disparities are primarily based on geographic location and socioeconomic status. 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, we need to develop and implement new and/or more effective policies that benefit everyone, including the most vulnerable and underserved populations.
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