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Environmentally induced cancer “grossly underestimated”? Doubtful.

The (U.S.) “President’s Cancer Panel” has released its 2008-2009 annual report, which includes a cover letter that says “the true burden of environmentally induced cancer has been grossly underestimated.” The report itself discusses exposures to various types of industrial chemicals, some of which are known carcinogens, in some detail, but gives nearly no data or analysis to suggest that these exposures are contributing to significant numbers of cancers. In fact, there is pretty good evidence that they are not.

U.S. male cancer mortality by year for various cancers

The plot above shows age-adjusted cancer mortality for men, by cancer type, in the U.S. The plot below shows the same for women. In both cases, the cancers with the highest mortality rates are shown, but not all cancers (e.g. brain cancer is not shown). For what it’s worth, I’m not sure how trustworthy the rates are from the 1930s — it seems possible that reporting, autopsies, or both, were less careful during the Great Depression — so I suggest focusing on the rates starting in about 1945. For both men and women, there are a few obvious features in these plots:

  1. a huge climb in lung and bronchial cancer mortality, starting later in women than in men (reflecting the pattern of smoking adoption);
  2. a big decline in stomach cancer mortality over the entire time period shown;
  3. substantial declines in colon and rectal cancer mortality over the past two to four decades (for men and women, respectively); and,
  4. very flat rates for most other cancers over at least the 50 years from 1945 to 1995.

U.S. male cancer mortality by year for various cancers

Note that there’s no sign of the famous “breast cancer epidemic” in the cancer mortality rates…nor of any other “epidemic” except lung and bronchial cancer, which are known to be smoking-induced. This is a strong argument against chemically-induced cancers being a major factor, because exposures to most of the chemicals mentioned in the President’s Cancer Panel report increased enormously between WWII and the 1990s.

Most of the claims of an “epidemic” of cancer are based on cancer “incidence,” which has indeed increased a lot, especially since the 1970s. But “incidence” in public health is like “significance” in statistics: it doesn’t mean the same thing as a term of art that it means in common speech. “Incidence” does not mean “the fraction of people who contract cancer,” as you might expect. It means “the fraction of people who are diagnosed with cancer.” Cancer awareness programs have been shown to increase cancer incidence: there’s a good example from Hawaii a decade or so ago, and a famous example of a jump in breast cancer incidence after First Lady Betty Ford announced that she had breast cancer and suggested that women should check themselves or have themselves checked. There is no question that cancer “incidence” has increased a lot since the 1950s. But there’s little or no evidence that more people are getting cancer (except lung and bronchial cancer).

In theory, one could argue that improvements in cancer treatment have exactly matched an increase in the number of people contracting cancer, such that the mortality rate stays steady (ovary, pancreas, leukemia, liver, breast) or goes down (colon and rectum, stomach), but that is not really a plausible argument over at least 40 or 50 years. It’s true that in the past ten years or so, medical treatment of many cancers has improved remarkably, but it cannot be true that treatment of many different cancers over fifty years happened to hold the mortality rate nearly constant.

It is possible that future cancer mortality, or the probability of getting cancer, will increase due to chemicals introduced in the past ten or twenty years — there is a lag between exposure and the development of cancer. But the data available to date do not support the claim that “the true burden of environmentally induced cancer has been grossly underestimated.”

There are plenty of other reasons to object to chemical exposures, of course. I hope the release of industrial chemicals to the environment, and human exposure through all routes, decreases substantially. But I don’t think it’s right to promote those goals, however laudable, through misstatements or misinterpretations of data, and I think that’s the case with the Cancer Panel report.


  1. Nick says:

    Charts aren't showing up…

  2. Mole people says:

    Tiff files don't fare too well on the internet.

  3. Jeremy Miles says:

    At least in my browser (Firefox) you need to right click where you expect to see the image, then choose "Show Image". Then the image appears in a new window. GIFs would make more people look at them though.

  4. Kaiser says:

    If you right click and view image, it shows up. It works for me anyway.
    But boy are the line charts ugly with very thick lines.

  5. zbicyclist says:

    Distorted facts are the mothers milk of fund raising.

    Who is this 3 member "Presidents Cancer Panel"? A heavily edited version of their bios on… shows that they have substantial interest in high levels of cancer funding.

    Dr. LaSalle Leffall … is past Chair of the Board, Susan G. Komen Breast Cancer Foundation (now Susan G. Komen for the Cure)

    Margaret L. Kripke …serves as a member of the External Advisory Board for the Southwest Biomedical Research Institute in San Antonio, the Advisory Committee of the Livestrong Survivorship Centers of Excellence, and Boards of Directors for 3 non-profit organizations in Houston.

    Abby B. Sandler, Ph.D., Chief, Institute Review Office (IRO), National Cancer Institute (NCI)… Before that, Dr. Sandler was a scientist for Pro-Virus, Inc. (now called Wellstat Biologics)

    Note even the American Cancer Society has raised questions about their conclusions: (… )

    "The American Cancer Society took issue with the report, describing it as provocative while perhaps overstating some risks at the expense of known causes of cancer, like tobacco, obesity, alcohol and sunlight."

  6. Megan Pledger says:

    The rates are age adjusted, it would be intersting to see the raw rates. Most western countries have an aging population so that there can be increases in the number of cancer patients with no change in the age adjusted rates.

  7. Bob O'H says:

    Hang on – you're arguing about factors affecting incidence of cancer by using death rates? I hope you can see why this is problematic.

  8. Phil says:

    Yes, the raw rates have indeed increased as the population has aged, as you guessed. I've seen those plots but not recently; you could look 'em up.

    Bob O'H,
    No, I don't see why using mortality is problematic, for reasons I discussed in the third-to-last paragraph of my post.

  9. digitalcat says:

    Hope this anonymous comment would show up (at work and can't sign up using work email) – it is not unreasonable to assume that age also correlates with accumulated exposure/absorption of known/unknown carcinogens, so one cannot rule out the possibility that the above graph of death rates adjusted for age may in fact remove some of the environmental effect over time.

  10. Bob O'H says:

    No, I don't see why using mortality is problematic, for reasons I discussed in the third-to-last paragraph of my post.
    Well, it does ignore any cancer in the figure which is declining.

    I'm also not convinced that the rates are flat. the ones that look flat are also the ones with a lower mortality, so a change of (say) a 5% increase won't look as big. IOW, you have a distortion due to the way the graph is drawn. If you eyeball the leukemia survival rates, you'll see that there is a decrease in mortality.

    Can you also provide a link explaining the methods used to calculate the incidence, to show that epidemiologists don't take under-reporting into account? I assume you did bother to check their methods first, before suggesting they were incompetent.

  11. Phil says:

    Bob O'H, Yes, I know a fair amount about incidence reporting and its shortcomings, having seen talks on the subject, read journal articles, and spoken with several epidemiologists about the issue. "Incidence" is not a good way to estimate the number of people who contract cancer.

    The claim to which I am objecting is that environmentally induced cancer (from exposure to industrial chemicals) is "grossly underestimated." I agree with you that a 5% increase in mortality in one of the less-common cancers might not show up on the plot above, and I would even agree that it's possible that some cancers may be 5% more common now than they used to be but the mortality figures don't show it because of better treatment. Could be. What I do not think is plausible is that, excluding smoking-induced lung cancers, total cancers or total cancer deaths are, say, 30% higher than they used to be, which would seem to be implied by saying that environmentally induced cancer is "grossly underestimated."

    If you want to argue that the plots are consistent with a slight increase in cancer due to increased environmental exposures to chemicals, especially in some of the less common cancers, then you'll have to find someone else to argue with, because I agree with you. But if you're saying that the figure is consistent with the "grossly underestimated" claim, then you can argue with me, because I think you're wrong.

  12. Nameless says:

    I wonder what's behind that massive decrease in stomach cancer death rates?