Douglas J. Myers1, Polly Hoppin2, Molly Jacobs2, Richard Clapp2 and David Kriebel2
1Department of Community and Environmental Health, College of Health
Sciences, Boise State University, 1910 University Drive, Idaho 83725 Boise, USA.
2Lowell Center for Sustainable Production, University of Massachusetts,
Lowell 1 University Avenue, 01854 Lowell, MA, USA.
A recent study examining the contribution of smoking to new cases of cancer has implications for cancer prevention priorities, in particular the importance of a “both/and” approach: both continuing to invest in reducing smoking and pursuing effective action to reduce other environmental carcinogens. The peer-reviewed study and follow-up analysis are here and here.
Controversy about the role of environmental hazards in cancer
Debates over the importance of “lifestyle” versus “environment” contributions to cancer have been going on for over 40 years. While there is consensus that cigarette smoking is an important risk factor, the contributions of environmental cancer-causing substances (carcinogens) in air, water and food remain moredisputed. Most cancer prevention messaging focuses on reducing cigarette smoking and changing other personal behaviors – including, diet, exercise, sun safety, and screening/early detection, with little mention of environmental carcinogens. This is despite widespread exposure to many known carcinogens and strong scientific evidence implicating their contribution to many types of cancer, including multiple systematic reviews of hundreds of peer-reviewed studies.
The reaction to the conclusions of a year-long study conducted by the U.S. President’s Cancer Panel (PCP) illuminates the controversy over how and whether information on environmental compounds and cancer should be used in cancer prevention initiatives.The Panel’s 2010 report “Reducing Environmental Cancer Risk” stated: “The burgeoning number and complexity of known or suspected environmental carcinogens compel us to act to protect public health, even though we may lack irrefutable proof of harm”. Some leading experts disagreed, arguing that the PCP was misguided in its emphasis on environmental carcinogens: “It is important not to detract from the fact that the major causes of cancer are smoking, overweight, and inactivity.”This controversy continues today. But if talking about environmental carcinogens “detracts” from attention to smoking, overweight and inactivity, the public, policy-makers and clinicians might be forgiven for concluding that all people need to do to prevent cancer is to change their unhealthy behaviors.
Study questions, methods and results
To inform decision-making on cancer prevention priorities, we evaluated the impact of smoking cessation on cancer rates.We were interested in investigating the role of changes in smoking habits on the incidence of cancer, and in particular we wanted to answer the hypothetical question: “Suppose smoking cessation were completely effective and smoking were entirely eliminated as a cause of cancer. How much cancer would still remain?”
To answer this question, we simulated the best possible case of a behavioral intervention to prevent cancer – the complete elimination of smoking – and then estimated the resulting reduction in cancer rates. We focused on cancer incidence of 12 types of cancer known to be linked to smoking; risk of other cancer types would not be affected by changes in smoking, and so we excluded them from our analyses. If smoking were eliminated, how much would cancer rates fall? Would this best-case scenario prevent the large majority of cancers for which smoking is a known risk factor? If not, perhaps additional modifiable risk factors should be sought and addressed.
We also exploredthese questions: How would the county-by-county variability in cancer rates of the 12 smoking-related cancer types be different if smoking werecompletely eliminated? Would all counties benefit equally from eliminating smoking? Would some counties still have high rates of cancers for reasons other than smoking? And would the 11-year downward trend in the 12 smoking-related types of cancer be different if smoking were completely eliminated? Would rates of new cases of cancer still be falling, or would progress be stalled?
To do our analyses, we usedcancer incidence data from 612 counties gathered in the National Cancer Institute’s Surveillance, Epidemiology and End Results Program (SEER) database 2006-2016, and county-level smoking data obtained from the Institute for Health Metrics and Evaluation (IHME)for 1996-2006. We investigated the impact of smoking cessation on the incidence of 12 cancer types for which smoking is a known risk factor by developingstatistical modelsto quantify the association between county-level smoking prevalence and cancer incidence, adjusting for age, gender, variability over time and among counties. We simulated complete smoking cessation, generated the cancer rates that would have occurred and compared them to actual rates.
The statistical models showed the expected strong association between smoking prevalence and cancer incidence. Simulating complete smoking cessationin 1996, the incidence of the 12 smoking-related cancer types in 2016 was 39.8% lower than actual rates. But not all counties were predicted to benefit equally from smoking elimination. The models estimated that if smoking had been completely eliminated, rates of cancer for which smoking is a known risk factor would have fallen less than 10% in some counties, many of them urban with elevated environmental exposures.For example, our follow-up analysis of lung cancer incidence rates in Allegheny County Pennsylvania, where high levels of air pollution and radon are a concern, concluded that lung cancer rates would have declined by 11%, compared to an average reduction in lung cancer rates across all counties of 62%.In addition, while the actual rates of all smoking-related cancers during the 2006 to 2016 time perioddeclined by almost 1% per year, under the scenario of smoking elimination, the trend in incidence of these cancer types was flat, not declining.
Our results can be summarized as follows. First, we estimated that about 60% of the cancers at tumor sites considered to be smoking-related would still occur even if smoking were completely eliminated. Second, the degree to which smoking elimination would reduce cancer incidence rates would not be uniformly distributed across the country. Our models predicted that some counties would have only modest reductions in cancer from eliminating smoking and by extension higher rates of cancers remaining. Third, under the same simulated condition of no smoking, the 11-year trend in the incidence rate of these 12 types of cancer would be stable – neither rising nor falling – indicating that smoking cessation is almost entirely responsible for the reductions in incidence that have occurred over this time periodand suggesting missed opportunities for other prevention strategies.
Conclusions and new directions
Overall cancer incidence in the U.S. has been falling over the past several decades. This has been attributed largely to the reduction in smoking prevalence, especially among men. Smoking prevention has produced dramatic reductions in cancer in the US for 12 major types of cancer. However, we estimate that eliminating smoking completely would not affect about 60% of cancer cases of the 12 smoking-related types, leaving no net improvement in the trend in new cases of cancer from 2006 to 2016. Smoking elimination would benefit some counties much less than others.
Without detracting from the importance of tobacco control, these findings suggest that progress in the primary prevention of cancer must include many strategies, not only those focused on healthy lifestyles. A particular opportunity is environmental chemicals which are ubiquitous and also elevated in particular states, regions and neighborhoods. Such exposures include radon, air pollutionfrom manufacturing facilities and vehicles, radioactiveand chemical contamination of air and water associated with oil and gas development, other contaminants in water and consumer products, pesticides, and chemical exposures in workplaces. Supporting these conclusions, other researchers have found a strong association between all-site cancer incidence and a measure of overall environmental quality, the Environmental Quality Index (which, developed by the U.S. EPA, combines measures of environmental quality in five domains: air, water, land, built environment and sociodemographic factors).
How might people and organizations concerned about cancer begin to take action onother cancer risk factors in addition to smoking, in particular environmental and occupational carcinogens? A first step is acknowledging the importance of these exposures as cancer prevention opportunitiesand providing and accessing information about steps that can be taken to reduce them. Expanding state cancer coalitions to include people with environmental expertise and lived experience of environmental exposures is another; these coalitions shape statewide cancer control plans. Leveraging the capacity of businesses already investing in safer alternatives and advocating for policies that incentivize a shift from reliance on toxic chemicals are also opportunities. We commend the Centers for Disease Control and National Association of Chronic Disease Directors for the recent launch of a webinar series for cancer prevention leaders on this topic which will provide examples of effective interventions and strategies for impactful partnerships and policies. And we applaud the research institutions, professional associations, non-governmental organizations and community groups that are elevating attention to the contribution of environmental and occupational chemicals to cancer and providing invaluable resources on these issues.
37
Smoking is a major cause
of 12 types of cancer.
If smoking were completely stopped, how much cancer
would remain?
October 2021
Continued on page 39 ...