Harvard Reports on Cancer Prevention
Volume II: Prevention of Cancer

Summary

The purpose of this second volume of the Harvard Report on Cancer Prevention is to set forth a framework for the prevention of cancer through reducing the major risk factors in the United States. Each chapter reviews the recent literature on strategies for prevention of specific cancer risk factors, and offers a consensus statement on what can be done through preventive services delivered by health care providers, through structural interventions implemented by government and industry, and through local activities to promote healthier environment and lifestyle.

Population changes in risk
A key conclusion of this report is that for prevention to be successful changes must be implemented through all components of the social strategy. Repeatedly, it has been seen that interventions that focus on only one component of the strategy fail or achieve only minimal shifts towards lower cancer risk. For major reductions in the burden of cancer to be achieved, we need broad-scale interventions that will shift the behavior of the whole population. Rather than focus solely on individuals defined as being at "high risk," a shift in behavior by the whole population can achieve greater reductions in cancer. Take for example activity and colon cancer. Lack of activity is now a defined cause of colon cancer.¹ However, the linear relation between increasing activity and lower risk of colon cancer means that even men and women who currently meet a specific national goal for activity can achieve further reduction in their risk of colon cancer by increasing their level of activity. Thus, rather than focusing solely on getting all individuals to meet the national goal, having the total population increase their weekly activity by the equivalent of 30 minutes of brisk walking per day would result in a greater reduction in the burden of colon cancer.

We estimate that if the entire population increased their level of physical activity by 30 minutes of brisk walking per day (or the equivalent energy expenditure, in other activities) we would observe a 15 percent reduction in the incidence of colon cancer. This reduction in colon cancer is predicted for both men and women, as the magnitude of the relation between physical activity and colon cancer is comparable across gender.² For the United States population, this translates to approximately 15,000 cases prevented per year. This assumes that even those who are already active increase their level. If, on the other hand, the 22 percent of the population who already meet the Year 2000 goals do not undertake any additional increase in their activity, then the overall benefits for the total population are substantially truncated. In addition, even those who increase their activity from currently low levels but who fail to reach the national goals will gain some substantial protection against colon cancer from the increase in activity.

As we note in the section on population level change in risk factors, most intervention studies have observed relatively small changes to date. Interpretation of these results however, must be placed in the context of the disease burd en of the entire population. Even small improvements in the distribution of risk factors for cancer translate into prevention of substantial numbers of new cancer diagnoses.

To achieve the goal of cancer prevention, strategies that fold the prevention efforts into our patterns of daily life, shifting social norms are more likely to be sustained. This emphasizes the importance of structural changes that support the prevention of cancer. Examples illustrated in this report include the regulation of indoor clean air which has contributed to the reduction in cigarette smoking through shifting social norms and increasing motivation for smoking cessation. Further, as noted in the section on addressing multiple risk factors simultaneously, we must increase our understanding of how to maximize the benefit of interventions when more than one risk factor is the focus of change. However, it is noteworthy that in parallel with such regulatory changes, messages from healthcare providers and behavioral interventions aimed at individuals have fostered the increase in smoking cessation among adults. Here and elsewhere in the report, we emphasize the need for coordinated interventions through all components of the framework to achieve reduction in the cancer burden. With the implementation of the strategies outlined in this report we can halve the incidence of cancer in the United States.

Tobacco
An estimated 30 percent of all US cancer deaths can be attributed to smoking.³ Thus, stemming the epidemic of tobacco smoking is our most effective means of preventing cancer.

Tobacco smoking causes cancer both by initiating cellular changes that lead to cancer, and through action late in the carcinogenic process, promoting the growth of tumors such as lung cancer. We therefore address smoking both in terms of adult cessation from smoking, and prevention of youth uptake of the habit. We conclude that the shift to a public health perspective on smoking cessation has resulted in a successful increase in the rate of cessation from smoking. Behavioral programs and pharmacotherapies such as nicotine replacement are the major individual level cessation strategies currently used. Health care provider advice and support along with community level regulations that support non-smoking norms can impact smoking cessation by enhancing motivation to quit and by preventing relapse among those who achieve initial cessation.

With regard to the initiation of smoking by America's youth, a comprehensive approach to smoking prevention is required. We need to integrate youth prevention into schools, community, media, and policy efforts to create an environment that consistently discourages tobacco use. A well-structured mass media campaign can be focused on youth and used to reinforce awareness and educational messages; to support school and community programs; encourage public debate on the cost, availability and promotion of tobacco, and to create a climate of support for policy changes that will discourage tobacco use.

Diet and obesity
An estimated 30 percent of all US cancer deaths can be attributed to diet in adult life, including its effect on obesity. Evidence indicates that a diet that reduces cancer risk should be high in fruit and vegetables, low in red meat, and low in salt.³

There is clear evidence that intensive educational and behavioral interventions are effective for teaching and persuading motivated individuals and small groups to change their diets. However, no single type of intervention has proven consistently successful. The most intensive strategies such as those implemented in clinical trials have produced the greatest effects on dietary change. The cost per person increases with greater intensity of the intervention. On the other hand, policy interventions and changes in food and nutrient supply have great potential to enhance the effect of individual focused interventions.

Sedentary lifestyle
Higher levels of physical activity can reduce the incidence of colon cancer and may help reduce the risk of breast and prostate cancers.³ Intervention approaches within worksites, schools, and by health care providers, have shown modest effects in increasing the physical activity level of participants, but many sites lack such programs. Public and environmental polices can powerfully encourage physical activity. Examples include the construction of sidewalks, bikeways and safe recreational spaces. Interventions can profitably aim to increase the entire distribution of physical activity in the populations, including reducing sedentary time as well as increasing moderate and vigorous physical activity.

Alcohol
Use of alcohol interacts with tobacco smoking in the causation of cancers of the upper respiratory and gastrointestinal tracts. Moreover, alcohol also causes cancer of the breast and large intestine.³ Because epidemiologic findings support a protective role of moderate drinking against cardiovascular disease, advice to minimize risk is complex. The US dietary guidelines recommend no more than one drink per day for women and no more than two drinks per day for men.⁴

School-based prevention education needs to be reinforced through a community-based coalition that seeks restrictions on irresponsible alcohol advertising and marketing, strict enforcement of laws to reduce youth access, and new polices to reduce alcohol availability, including higher excise taxes. In addition to providing prevention messages, mass media campaigns can be used to enhance school based and community programs, encouraging public debate on policy initiatives to reduce alcoh ol consumption, and publicize new laws and regulations or increased enforcement efforts. Community wide responsible beverage service programs, for example, can be effective in preventing alcohol service to minors, decreasing the number of patrons who become intoxicated, and preventing those who are impaired to drive.

Viruses and infectious agents
Overlooked as a cause of cancer until the recent past, infectious agents are now considered as the cause of approximately five percent of cancers in the US.³ Among the more significant agents are human papilloma viruses (HPV), which cause cancer of the uterine cervix, and hepatitis B virus (HBV) which causes in liver cancer. Sexually transmitted viruses are a major preventable cause of cancer. Primary prevention can be achieved through delaying onset of sexual activity, abstaining from sex with individuals not known to be infection free, regularly using latex condoms, and being vaccinated against hepatitis B. Secondary prevention is possible through screening, early detection and treatment of cervical cancer.

Occupational factors
The control of occupational exposure to carcinogens in the US represents an important triumph in the primary prevention of cancer. Collectively, occupational factors are thought to cause about five percent of cancer deaths, mostly of the lung, bladder, and bone marrow.³ Application of a systematic hierarchy of controls is effective in reducing this risk of occupational exposure to carcinogens. Manufacturers, employers, workers, unions, healthcare providers, and occupational health professionals all play important roles in workplace cancer prevention. Regulatory standard setting and enforcement are an essential complement to voluntary efforts.

Socioeconomic status
Cancers of the lung, stomach, uterine cervix, and possibly others as well are particularly common among poor and underprivileged population groups. Poverty may be though of as an important underlying cause for these cancers since it is associated with increased exposure to tobacco smoke, alcoholism, poor nutrition, and certain infectious agents. The primary prevention of cancer among the poor ultimately depends on altering the social environment that systematically stratifies cancer risk according to socioeconomic position.

Sun exposure
Melanoma rates have risen rapidly in the US over the past 40 years. Childhood and adolescent sun exposure is the major cause of melanoma. Campaigns such as that implemented in Australia to reduce exposure to the sun between 11am and 3 PM, to increase the use of broad brimmed hats, to use sunscreen with SPF15 or higher, have also emphasized community level support for apparently individual changes. Town regulations have been modified to increase access to shade at town swimming pools, public awareness of sun exposure has been increased through collaboration with the national weather service, and now architects compete annually for design awards that reward sun protection in building design. A multi-pronged approach has dramatically shifted social norms, reduced high-risk behavior, and the number of sunburns reported among children and adolescents has decreased.

Conclusion
Although we cannot pretend that preventing cancer deaths in the US will be easy, the broad individual and social changes that must occur are outlined in this report. Change is possible. Rates of smoking have halved among men since the first report of the Surgeon General on smoking in 1966. Rates in women have declined since peaking in 1960. Dietary change has also been substantial. Our challenge is to harness the knowledge that we have about cancer risk and use this to our collective advantage. We know that cancer risk is malleable. Rates of cancer have changed over time and within populations upon migration and following change in lifestyle. Implementing the strategies outlined in this report we believe could reduce the burden of cancer in the US by 50 percent. We have substantial knowledge about the causes of human cancer. This report summarizes a broad range of social strategies to implement cancer prevention. We require the political will to make resources available to implement these strategies. Currently only five percent of the national health expenditure, which exceeds one trillion dollars annually, are allocated to prevention.

Our ability to prioritize strategies for cancer prevention would be enhanced by rigorous cost-effectiveness evaluations of both primary and secondary prevention. To date, insufficient resources have been allocated to this avenue of inquiry. Hence, we are left to informally weight the likely benefit of prevention efforts, the time frame from intervention to observed benefit, and the magnitude of the lifestyle or regulatory change that can be achieved. Because cigarette smoking remains the leading cause of cancer, efforts addressing the prevention of adolescent smoking and cessation from smoking among adults, must be our highest priority in cancer prevention. Adding greater public awareness of other strategies for cancer prevention as outlined in this report should add hope and speed widespread modification to lifestyles that will result in lower cancer risk and overall healthier lifestyle. Change in diet, increase in physical activity, reduction in alcohol intake, and improved contraceptive practices can each be implemented now. The benefits will be maximized when strategies are implemented concurrently through health care providers, through regulatory changes, and through individual and community level changes.

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