Does discussion of environmental causes of cancer cause cancer?

July 4, 2012 at 1:32 pm | Posted in Feature Articles | 1 Comment

There is no obvious reason why the 2010 US President’s Cancer Panel examination of chemicals as potential, under-discussed causes of cancer should have caused so much controversy. The report was hardly unheralded, and the recommendations were in line with much existing cancer prevention strategy. The conclusion that one is forced to, is critics of the report must believe that discussing environmental causes of cancer undermines cancer prevention strategy: in other words, that talk about environmental causes of cancer causes cancer.

Interest in chemicals as a cause of cancer

Although there has long been concern that chemicals may cause cancer, there has been little mainstream interest in the possibility that low-level exposure to chemicals, as environmental pollutants or present in consumer goods, may be increase an individual’s risk of getting cancer.

In fact, very little has changed in the 30 years since epidemiologists Richard Doll and Richard Peto published their seminal 1981 paper in which they attributed 9% of cancers to environmental causes. Doll and Peto’s attribution of 4% of cancers caused by occupation and 5% by pollution and geographical location has makes environmental causes of cancer look a very low priority in comparison to other risk factors (Doll & Peto 1981).

Interest in the place of chemicals in cancer preventions strategies did, however, spike in 2010 with the publication of the US President’s Cancer Panel report on priorities for cancer prevention (PCP 2010). The report voiced scepticism about how certain we can be about the contribution to cancer rates of chemicals in our everyday environment, given how few chemicals are tested for carcinogenicity.

The report also made a sweeping set of policy recommendations to ameliorate any potential harm being done by a chemicals industry it regarded as inadequately regulated, while acknowledging how the lack of data makes it difficult to quantify the health benefits of such regulation.

Conflict with a lifestyle-focused establishment

At first sight, the PCP report should seem innocuous. It is normal for reports on cancer policy to highlight data gaps and recommend more research, and for the PCP report to also urge improvement in US chemicals regulation was hardly unprecedented, especially in the context of the EU’s implementation of REACH and increasing public concern about the safety of the chemicals to which people are exposed on a daily basis.

Any appearance of innocuousness was, however, dispelled by harsh criticism from the cancer establishment. In a statement by the American Cancer Society (ACS), Michael Thun MD, Vice President Emeritus at Epidemiology & Surveillance Research, described the report as “unbalanced by its implication that pollution is the major cause of cancer, and by its dismissal of cancer prevention efforts aimed at the major known causes of cancer (tobacco, obesity, alcohol, infections, hormones, sunlight) as ‘focussed narrowly.’” (ACS 2010)

Thun is clearly unhappy that the report looks at something other than lifestyle causes of cancer. Although there has been no such report in the UK to crystallise lifestyle-centric positions on cancer prevention, there is a clear and long-standing emphasis on lifestyle and behaviour in UK cancer prevention strategy.

For example, the UK Cancer Reform Strategy states: “Over half of all cancers could be prevented by changes to lifestyle. Taking cross-government action to tackle the major risk factors for cancer, improving awareness and encouraging people to adopt healthy lifestyles is therefore crucial to improving cancer outcomes.” (Department of Health 2007, p6)

Cancer Research UK, in the prevention section of its website, emphasises healthy weight, not smoking, being physically active, eating a healthy diet and being sun-safe (CRUK 2012a). This is consistent with the CRUK analysis of attributable causes of cancer published late last year, finding that 40% of cancers can be prevented by lifestyle and behavioural changes. (Parkin 2011)

In this context, environmental factors are of distant importance. Are the PCP recommendations therefore controversial because they stand counter to a position that a person’s lifestyle comprises the major risk factors for cancer, and that modifying an individual’s behaviour are key to cancer prevention?

Cancer prevention is not, in reality, exclusively focused on lifestyle

If individual risk factors really were the most important thing in cancer prevention, one would expect cancer prevention strategy to focus exclusively on these. However, cancer prevention strategies target both individual behaviours and the societal context which affects an individual’s cancer risk.

On alcohol, the UK Cancer Reform Strategy sets out a highly individualist programme, to help people identify when they are drinking too much and then do something about it, “including a sustained national communications campaign to […] ensure everyone has the information they need to estimate how much they drink [and provide] targeted information and advice for people who drink at harmful levels.”

On tobacco, however, the Strategy sets out a contrasting set of societal interventions: “As well as maintaining the high price of tobacco and taking action to reduce the availability of illicit tobacco, the government will consult during Spring 2008 on proposals for the next steps in tobacco control and the further regulation of tobacco products, including the display of tobacco at the point of sale, access to tobacco from vending machines and packaging.”

CRUK’s campaign to introduce plain tobacco packaging is a clear example of targeting the appeal of tobacco products rather than an individual’s choices about consuming them, the aim being “to reduce the number of teenagers who start smoking which will result in a gradual, long-term reduction in sales” by placing further restrictions on the marketing of tobacco itself, rather than trying to change how people respond to that marketing (CRUK 2012b).

The UK’s introduction of a vaccination programme to immunise girls against some strains of the human papilloma virus is another example of an intervention difficult to classify as targeted at an individual’s behaviour, with the lack of immunity rather than a person’s sexual practices being seen as the strategic root of the problem.

So although “improving awareness and encouraging people to adopt healthy lifestyles” is held as “crucial”, cancer prevention strategies are much broader in choice of target than Thun’s comments and CRUK’s public emphasis on lifestyle choices would imply.

As a recommendation to limit exposure to harmful substances in the environment, the PCP recommendations appear a natural extension of the realities of cancer prevention strategies – so why are they not perceived as such? What upset Thun?

What makes the hostility to the PCP report all the more confusing are comments from Thun himself, reported in the New York Times, saying that the ACS “shared the panel’s concerns about people’s exposure to so many chemicals, the lack of information about chemicals, the vulnerability of children and the radiation risks from medical imaging tests”. (NYT 2010)

The ACS voiced these concerns in 2009, saying: “New strategies for toxicity testing, including the assessment of carcinogenicity, should be implemented that will more effectively and efficiently screen the large number of chemicals to which people are exposed.” (Elizabeth et al. 2009)

Discussion of environmental causes of cancer “a distraction”

Other comments on the PCP report look to provide insight but ultimately only furnish us with further confusion. Graham Colditz MD PhD, Associate Professor for Prevention and Control at the Siteman Cancer Center, Washington University School of Medicine,  said: “The damage is that it distracts us, as a society, from actually acting on the things that are already in our grasp.” He “take[s] tobacco as the best example” with more than 20% of Americans still smoking “despite nearly 50 years of cancer warnings”. (Reuters 2010)

As we reported in our coverage of the BJOC report, measurable, modifiable risk factors are central to cancer prevention strategy. For the PCP to imply that tobacco use, causing 25-30% of cancer, is not a major issue in cancer prevention would be startling – but then the PCP never says tobacco is unimportant. Indeed, three years previously, the PCP report (with two of the same authors) looked at this in detail (PCP 2007, PDF).

Several commentators confess to a failure to understand where Colditz sees the contradiction (Holzman 2010), “given that the very point of the report was to focus on an aspect of cancer prevention that the Panel considered to have been historically underrepresented” (Orac 2010).

There are other inconsistencies implied in Colditz’s statement: if environmental causes of cancer are a distraction because they are relatively insignificant next to tobacco, then what would he have to say about alcohol or human papilloma virus (HPV)? HPV in particular causes relatively few cancers, with cervical cancer rates at 8.1 per 100,000 people by 2003 in the UK, down 49% from 1971, even before the introduction of HPV vaccination.

On pure numbers, it is hard to see why Colditz should not also classify this as a distraction. Nor is it likely that Colditz is arguing against research into causes of cancer, otherwise where would the HPV vaccine have come from in the first place?

The clue, perhaps, lies in the word “distract”, and Colditz’s statement that: “The lack of physical activity, weight gain, obesity clearly account for 20% or more of cancer in the United States today.” The report, he said, “gives people an excuse to ignore the risk factors most in their control” (Reuters 2010, our emphasis). In other words: talking about the causes of cancer causes cancer.

Disinhibition: does talking about causes of cancer, cause cancer?

Arguably, what Colditz and Thun are really worried about is disinhibition, defined by the US Center for Disease Control as “an increase in unsafe behaviors in response to perceptions of safety caused by introduction of a preventive or therapeutic intervention.” For example, this might take the form of an individual engaging in unsafe sex because of the ready availability of anti-retroviral treatments for HIV.

In the published literature, disinhibition seems to be considered mainly in relation to communicable disease, and sexually transmitted diseases in particular, with research into HPV vaccination (e.g. Schuler et al. 2011) and HIV prevention (e.g. Hogben & Liddon 2008).

Excepting HPV, however, there appears to be no formal discussion of disinhibition when it comes to behaviours which increase someone’s risk of cancer. Nobody has argued that discussion of genetic causes of cancer undermines cancer prevention, while for HPV the risk of disinhibition was considered negligible and manageable (Gibbs 2006). Few people in the medical profession argued against rolling out the vaccine and recent research has indicated such fears of disinhibition were unfounded (Liddon et al. 2012).

What we therefore appear to have in the implied positions of Colditz and Thun are inconsistently applied concerns about disinhibition: while there are occasions on which it is assumed that discussion of a non-lifestyle cause of cancer is seen as harmless (such as for HPV or genetics), there are also occasions, such as in discussion of chemicals, where disinhibition is seen as important.

Since neither concern, nor lack thereof, seems to be based on factual evidence that discussion of causes of cancer has a disinhibiting effect on behaviours associate with cancer risk, there is no reason to conclude that Thun and Colditz’s forbidding of discussion is the best approach to managing discussion of environmental causes of cancer.

There are also practical considerations at play. For one thing, the information is out there and being discussed. Disinhibition caused by awareness of potential environmental causes of cancer (if it is happening) must be happening anyway, so it is likely better to manage the discussion than deny the importance of any putative links between the environment and cancer. Otherwise, one is in danger of sitting like Cnut with a hand up at the incoming tide.

Secondly, if the PCP is right and the environment is potentially an important contributor to cancer incidence, then we have new opportunities for preventing cancer. It would then be rather odd to communicate in such a way as to set a social context in which inhibits the creation of opportunities for their further exploration, especially if these opportunities are consistent with approaches already in use.

Conclusion

When it comes to debating where policy ought to go, it does not seem to be helpful to fail to distinguish between how one ought to communicate about environmental risk factors, and what those risk factors are. When one is obscuring the other, how can public debate be clear?

Margaret Kripke, PhD, of the President’s Cancer Panel reports participating in an interview in which a questioner said they had never smoked in their life, had run marathons, had no family history of cancer, and yet had cancer anyway. Kripke says: “What about these people?” (Kripke 2012)

If the debate is not clear, it is hard to comprehend how can cancer prevention strategies which serve the majority of people, who get cancer in spite of avoiding the lifestyle risk factors, can be developed and obtain recognition.

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  1. […] Does discussion of environmental causes of cancer cause cancer? There is no obvious reason why the 2010 US President’s Cancer Panel examination of chemicals as potential, under-discussed causes of cancer should have caused so much controversy. The report was hardly unheralded while the recommendations were in line with much existing cancer prevention strategy. The conclusion that one is forced to, is critics of the report must believe that discussing environmental causes of cancer undermines cancer prevention strategy: in other words, that talk about environmental causes of cancer causes cancer. (July 2012) […]


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