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