Preventing Cancer from Developing
Cancer Progress Report 2015: Contents
In this section you will learn:
More than half of U.S. cancer deaths are a result of preventable causes.
Not using tobacco is the single best way a person can prevent cancer from developing.
Up to one-third of all new cancer diagnoses in the United States are related to being overweight or obese, physical inactivity, and/or poor dietary habits.
Many cases of skin cancer could be prevented by protecting the skin from ultraviolet radiation from the sun and indoor tanning devices.
Infection with many known cancer-causing pathogens can be prevented by vaccination or managed by treatment.
Developing a personalized cancer prevention and early detection plan with your health care practitioners can help prevent cancer before it starts or intercept it early in its development, when it can be more easily and successfully treated.
Factors that increase the chance that a cell will acquire a genetic mutation consequently increase the chance that a cell will become cancerous and are referred to as cancer risk factors (see sidebar on
Why Me? Why This Cancer?). Decades of research have led to the identification of many cancer risk factors (see
Figure 8), which, in turn, has taught us that many cases of cancer are preventable (34).
In the United States, many of the greatest reductions in cancer morbidity and mortality have been achieved by translating discoveries of cancer risk factors into effective new public education and policy initiatives. For example, major public education and policy initiatives to combat cigarette smoking have been credited with preventing eight million premature deaths from 1964 to 2014 (35) (see
Figure 9), and policy initiatives that minimize exposure to other cancer risk factors, such as asbestos and pollutants, have also played a role.
Policies, whether implemented by schools, workplaces, businesses, or government—local, state, or federal—work by helping to create environments that allow individuals to more easily adopt a lifestyle that promotes cancer prevention. Thus, it is imperative that everyone work together to develop and implement new, more effective public education and policy initiatives to help reduce the burden of cancer further, in particular the burden from those cancers related to preventable causes.
In addition, a great deal more research and more resources are needed to understand why some individuals are refractory to public education and policy initiatives and how best to help these individuals eliminate or reduce their risk of some cancers.
Eliminate Tobacco Use
Tobacco use is responsible for almost 30 percent of cancers diagnosed in the United States each year (34) (see
Figure 8). Therefore, one of the most effective ways a person can lower their risk of developing cancer, as well as other smoking-related conditions such as cardiovascular, metabolic, and lung diseases, is to eliminate tobacco use (see sidebar on
Reasons to Eliminate Tobacco Use).
Since the relationship between tobacco use and cancer was first brought to the public’s attention in 1964, when the “U.S. Surgeon General’s Report on Smoking and Health” was published (43), the development and implementation of major public education and policy initiatives have more than halved cigarette smoking rates among U.S. adults (36) (see
Figure 9). As a result of these reductions, an estimated 800,000 deaths from lung cancer were avoided between 1975 and 2000 (36).
Unfortunately, U.S. cigarette smoking rates have begun to plateau in recent years (36), and 831,000 individuals age 12 or older began smoking cigarettes daily in 2013 (44). If we continue on this path, researchers estimate that 5.6 million children currently ages 0 to 17 years will die prematurely of smoking-related illnesses, including cancer (36).
Globally, tobacco use was estimated to be responsible for about six million deaths in 2011, and this number is projected to reach eight million in 2030 if current trends continue (45). Given that there were an estimated 1.6 million lung cancer deaths worldwide in 2012 (6), and that the majority of these deaths are attributable to tobacco use, it is clear that tobacco-related lung cancer is responsible for more than one million deaths around the world each year.
Cigarettes are not the only tobacco products that can cause cancer—smoking cigars, using smokeless tobacco (for example, chewing tobacco and snuff), and smoking tobacco in pipes have all been linked to certain types of cancer (38, 39). Given that in the United States, in 2013, there were an estimated 12.4 million current cigar users age 12 or older, 8.8 million smokeless tobacco users, and 2.3 million pipe tobacco users, in addition to the 55.8 million cigarette smokers (44), it is imperative that researchers, clinicians, advocates, regulators, and policymakers continue to work together to develop new and better approaches to prevent tobacco use initiation and facilitate cessation if we are to eradicate one of the biggest threats to public health.
Electronic cigarettes (e-cigarettes) are frequently marketed as a less harmful alternative to traditional combustible cigarettes and as helpful for those trying to quit cigarette smoking (47). However, e-cigarettes may be harmful if they increase the likelihood that nonsmokers—particularly children—or former smokers will start smoking combustible cigarettes, or if they discourage smokers from quitting. Therefore, more research is needed so that we can fully understand the health consequences of e-cigarette use, their value as tobacco cessation aids, and their effects on the use of combustible tobacco products by smokers and nonsmokers (41) (see sidebar on
E-cigarettes: What We Know and What We Need to Know). The need for this information is particularly pressing because recent data show that in 2014, e-cigarettes were the most commonly used tobacco product among U.S. middle and high school students, with use of these devices tripling from 2013 to 2014 (48).
Maintain a Healthy Weight, Eat a Healthy Diet, and Stay Active
Researchers estimate that one in every three new cases of cancer diagnosed in the United States is related to being overweight or obese, being inactive, and/or consuming a poor diet (15, 34). Therefore, maintaining a healthy weight, participating in regular physical activity, and eating a balanced diet are effective ways people can lower their risk of developing or dying from cancer (49) (see sidebar on
Reduce Your Risk for Cancers Linked to being Overweight or Obese, Being Inactive, and/or Consuming a Poor Diet). In fact, two recent studies that followed 650,000 individuals for more than 10 years showed that healthy lifestyles reduced cancer incidence by 10–15 percent, and cancer mortality by 20–25 percent, in addition to 40–50 percent reductions in cardiovascular-associated mortality and 25–40 percent reductions in all-cause mortality (50, 51).
In addition to the fact that being overweight or obese as an adult has been strongly associated with 10 types of cancer (15, 54-56) (see
Figure 10), recent data suggest that increased body weight during childhood and adolescence may increase risk for colorectal cancer later in life (57, 58). Larger studies are needed to confirm this finding and investigate whether early-life excess body weight increases risk of other types of cancer.
Given that being overweight or obese and being inactive have such an immense impact on cancer risk, as well as risk for other diseases, it is extremely concerning that in the United States more than two-thirds of adults are overweight or obese (59), 17 percent of youth are obese (60), and nearly half of all adults do not meet the recommended guidelines for aerobic physical activity (61). Unfortunately, the United States is not alone; the latest estimates show that 20 percent or more of the population age 15 or older of nine other Organization for Economic Cooperation and Development (OECD) countries is obese (62) (see
Figure 11). Moreover, sedentary behaviors, such as prolonged sitting at a computer, may increase risk for certain types of cancer (63), although additional research is needed to more clearly define the contribution of sedentary behavior to risk for cancer.
Thus, concerted efforts by individuals, families, communities, schools, workplaces, institutions, health care professionals, media, industry, government, and multinational bodies are required to develop and implement effective strategies to promote the maintenance of a healthy weight and the participation in regular physical activity. Although this will enhance overall health, more research is required to better understand the effect of weight loss at various stages of life on cancer risk.
In addition to preventing the development of some cancers, maintaining a healthy weight, engaging in regular physical activity, and eating a balanced diet may also improve outcomes for individuals diagnosed with certain types of cancer, in particular breast, colorectal, and prostate cancers; reduce risk of disease recurrence and metastasis; and increase the chance of long-term survival (65-68).
Protect Skin From UV Exposure
Most cases of the three main types of skin cancer—basal cell carcinoma, squamous cell carcinoma, and melanoma—are caused by exposure to ultraviolet (UV) radiation from the sun, sunlamps, sunbeds, and tanning booths (69). In fact, it has been estimated that UV exposure causes as many as 90 percent of U.S. cases of melanoma, the most deadly type of skin cancer (69). Although the majority of these cases are caused by UV radiation exposure from the sun, about 8 percent are attributable to indoor tanning (70). Thus, one of the most effective ways a person can reduce their risk of skin cancer is by protecting themselves from the sun and not using UV indoor tanning devices (see sidebar on
Ways to Protect Your Skin).
Despite this knowledge, melanoma incidence rates in the United States have been increasing for at least three decades, and the number of new cases of melanoma diagnosed each year is projected to rise from 65,647 in 2011 to 112,000 in 2030 if current trends continue (71). Fueling the rise is the fact that one in three adults in the United States reports experiencing at least one sunburn in the past 12 months, and 5 percent report using an indoor UV tanning device at least once (72, 73). Moreover, 13 percent of all high school students and 31 percent of white high school girls report using an indoor UV tanning device in the past year (74).
Given these continued exposures and that fewer than 15 percent of men and 30 percent of women use sunscreen regularly on their face and other exposed skin when outside for more than one hour (75), it is vital that all sectors of the U.S. population work together to develop and implement more effective policy changes and public education campaigns to reduce exposure to UV radiation. In fact, it is estimated that implementation of a comprehensive skin cancer prevention program could prevent about 21,000 melanoma cases each year from 2020 to 2030 (71). Moreover, with nearly 5 million people a year treated for all forms of skin cancer in the United States at an estimated cost of $8.1 billion (69), these efforts are vital if we are to reduce the personal and the economic burden of skin cancer.
Prevent Infection With Cancer-causing Pathogens
Persistent infection with a number of pathogens—bacteria, viruses, and parasites that cause disease—is responsible for an estimated 16 percent of worldwide cancer cases diagnosed each year (76-78) (see
Table 4, and
Figure 12). 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.
In fact, there are strategies available to eliminate, treat, or prevent infection with the four pathogens that account for more than 90 percent of pathogen-associated cases of cancer: Helicobacter pylori, hepatitis B virus (HBV), hepatitis C virus (HCV), and human papillomavirus (HPV) (78) (see sidebar on
Preventing or Eliminating Infection With Cancer-causing Pathogens). Thus, it is clear that these strategies are not being used optimally and that the global burden of cancer could be significantly reduced through more effective implementation of these strategies.
In the United States, the development of strategies to increase uptake of the three FDA-approved HPV vaccines could have an immense impact on cancer prevention (see
Cancer Interception, Detection, and Diagnosis). The most recent estimates from the Centers for Disease Control and Prevention (CDC) show that in 2013, only 6 percent of men and 37 percent of women ages 19 to 26 had received one or more dose of HPV vaccine (79). In addition, in 2012, only 33 percent of girls ages 13 to 17 had received the recommended three doses of HPV vaccine (80). This low coverage stands in stark contrast to that in other high-income countries, such as Australia and the United Kingdom, and Rwanda, a low-income country that recently reported HPV vaccination of more than 90 percent of eligible girls following implementation of a national, multisector, collaborative, school-based program (81, 82).
Moreover, it is estimated that in the United States, more than 50,000 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 (82). In addition, research has shown that vaccinating boys as well as girls has the potential not only to save lives from oropharyngeal cancer, but also to save health care costs (83).
Limit Exposure to Other Risk Factors
There are numerous additional cancer risk factors, including reproductive factors, occupational cancer-causing agents, and environmental pollutants (84) (see
Figure 8). Given that it can be difficult for people to avoid or reduce their exposure to many of these factors, it is imperative that policies are put in place to ensure that everyone lives in a safe and healthy environment.
In the United States, some policies that help prevent cancer 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 (85). For other known environmental cancer risk factors, for example, radon gas released from rocks, soil, and building materials, there are existing guidelines for reducing exposure, but compliance with these guidelines is not mandatory. For others, for example, exposure to occupational cancer-causing agents and environmental pollutants, there is a clear need to develop and implement more effective policies.
One environmental pollutant that was recently classified by the International Agency for Research on Cancer (IARC), an affiliate of the World Health Organization, as “carcinogenic to humans,” alongside agents such as plutonium and cigarettes, is outdoor air pollution (87).
Outdoor air pollution is a complex cancer-risk factor because it is a mixture of pollutants, some of which are currently classified as carcinogenic to humans by IARC, that vary over space and time as a result of differences in climate and sources of outdoor air pollution. However, we know 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 sorely needed if we are to reduce the global burden of cancer.
Screening for Early Detection and Interception
We know that most cancers arise as a result of the accumulation of genetic mutations and that the chance that a cell acquires a genetic mutation is influenced by many different factors (see sidebar on
Why Me? Why This Cancer?). Although people can avoid some of these factors, thereby significantly reducing their risk for cancer, not all factors are avoidable—for example, the acquisition of mutations during cell multiplication (21)—and not everyone avoids factors that can be avoided. This is where we have learned to exploit our knowledge of the causes, timing, sequence, and frequency of the genetic, molecular, and cellular changes that drive cancer initiation and development to implement screening strategies that allow us to intercept these events at the earliest possible stage.
Some screening tests can prevent cancer from developing because they detect precancerous changes in a tissue that can be intercepted and removed before they have the chance to develop into cancer. For example, colonoscopy can detect abnormal growths, or polyps, in the colon and rectum that can be removed before they develop into colorectal cancer. In fact, the CDC estimates that between 2003 and 2007, approximately 33,000 cases of colorectal cancer in the United States were prevented by colorectal cancer screening (88).
Other screening tests can detect cancer at a very early stage of development so that it can be intercepted before it has spread to other parts of the body, which makes it more likely that a patient can be treated successfully.
Screening to detect and intercept cancer before an individual shows signs or symptoms of the disease for which he or she is being screened has many benefits, but it can also result in unintended adverse consequences (see sidebar on
Cancer Screening). Thus, population-level use of a cancer screening test must not only decrease deaths from the screened cancer, but it must also provide benefits that outweigh the potential risks. Determining whether broad implementation of a screening test can achieve these two goals requires extensive research and careful analysis of the data generated.
In the United States, rigorous data analysis by members of the U.S. Preventive Services Task Force (USPSTF)—an independent group of experts convened by the Public Health Service—has led to evidence-based recommendations for the use of screening tests for four types of cancer among the general U.S. population (see sidebar on
USPSTF Cancer-screening Recommendations for Average-risk Adults). These recommendations are re-evaluated as new research becomes available and can be revised if deemed necessary.
The USPSTF and other relevant professional societies’ evidence-based cancer screening recommendations are only one consideration when a person makes decisions about which cancers he or she should be screened for and when. This is because everybody has his or her own unique risks for developing each type of cancer, and the established screening guidelines apply to average-risk individuals. A person’s overall risks are determined by genetic, molecular, cellular, and tissue makeup, as well as by lifetime exposures to cancer risk factors (see
Figure 8). Therefore, every individual should consult with his or her health care practitioners to develop a cancer prevention and early detection plan tailored to their personal cancer risks. Given that risk for different types of cancer can vary over time—for example, risk for most cancers increases with age—it is important that individuals continually evaluate their personal screening plans and update them if necessary.
A New Era of Precision Prevention and Interception
As we develop and implement new strategies that pair our increased molecular understanding of cancer development with knowledge of an individual’s unique cancer risk profile, including their genetic makeup at birth, exposures to cancer-risk factors, age, and gender, we will usher in a new era of precision prevention and interception (89) (see
Precision prevention and interception are not entirely new concepts. For example, we know that some individuals are at increased risk of certain cancers because they inherited a cancer-predisposing genetic mutation (see
Table 5). If a person thinks that that they are at high risk for developing an inherited cancer (see sidebar on
How Do I Know If I Am at High Risk for Developing an Inherited Cancer?), he or she should consult a physician and consider genetic testing, and if the person does indeed carry one of these mutations, risk-reducing measures tailored to his or her precise needs can be taken (see sidebar on
Direct-to-Consumer Genetic Testing). Some people at high risk might be able to reduce their risk of developing cancer by modifying their behaviors, whereas others might need to increase their participation in screening programs or consider taking a preventive medicine or having risk-reducing surgery (see
Table 6 and
Appendix Table 2).
Despite the progress that has been made in cancer prevention, early detection, and interception, not all cancers are currently preventable and not everyone has access to or takes advantage of current prevention and early detection strategies. Moreover, these strategies are not equally effective for all individuals.
Precision prevention and interception have the potential to address these issues and to significantly reduce the personal and financial burdens of cancer. However, achieving this potential will require input from researchers across the spectrum of biomedical research.
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Progress Report 2015 Contents