The government is not doing a good job in telling us what causes cancer.
Cancer is the second leading cause of death in the
This week the NTP released the "Eleventh Edition of the Report on Carcinogens." Unfortunately, this report adds no clarity to the question of what causes human cancer -- and only adds to the current confusion and misunderstanding.
Within the medical specialty of epidemiology -- the study of the causes and distribution of human disease in a population -- there is the sub-specialty of cancer epidemiology. There are thick textbooks and a multitude of professional journals replete with information on what causes cancer. Were a government agency to distill this information on causation and risk factors for cancer in a consumer-friendly, practical way, it would allow Americans to take a hands-on approach to reducing cancer risk. Ultimately such information could lead to a substantial decrease in cancer mortality.
Unfortunately, however, the "cancer causation" lists as prepared by the National Toxicology Program and released this week are misleading, out of context and irrelevant to 99% of Americans and. One might legitimately argue that the NTP "cancer list" actually does more harm than good by a) overwhelming us with "background noise" about cancer causation, thus diverting our attention from the real, preventable causes of cancer; b) deterring us from using pharmaceuticals that promote overall good health, despite the fact that they may also present a small risk of cancer; and c) providing fodder for mischief by those who wish to terrorize us about the alleged cancer risk of trace levels of synthetic environmental chemicals.
There are four major defects in the NTP cancer list.
First, the lists of "substances, mixtures or exposures...known to be human carcinogens" and its counterpart list of exposures "reasonably anticipated to be human carcinogens" are prepared primarily by committees of toxicologists -- not cancer epidemiologists.
Toxicology is a noble profession and contributes to our understating of the safety and efficacy of various chemicals in our lives, including food additives, drugs and cosmetics. Toxicologists, however, do not study people; the subjects of their studies are laboratory animals. On the other hand, cancer epidemiologists do study human populations. For that reason alone, advice on what does or might cause cancer should be coming from the National Cancer Institute, not the National Toxicology Program.
Second, a large number of chemical substances listed on the "known" and "maybe" lists have zero relevance to the lives of the overwhelming majority of Americans. For example, ethylene oxide (a chemical used to make other chemicals and also used in the health care industry to sterilize medical devices) and cadmium (used in the manufacture of batteries) are listed as "known" carcinogens. We are also told that tetrafluoroethylene (used in the production of polymers) and trichlorethylene (used as a degreaser for metal parts) are "likely" to be human carcinogens. Almost none of us will ever have any occupational exposure to these chemicals, and the fraction of a percent of those who do have such exposure will not be at increased risk of cancer because exposure levels in the workplace are by law exceedingly low.
Third, and most offensive, the NTP groups the major preventable causes of cancer together with the purely hypothetical risks noted above. "Tobacco smoking" is slipped in there on the "known" list along with risks that have no relevance to the general population: cadmium, crystalline silica, 1,3 Butadene and "dyes metabolized to benzidine." There is no clue in the NTP "cancer causation guide" that these chemicals account for approximately 0% of cancer causation today -- while tobacco use accounts for nearly 40% of cancer mortality annually in the
Fourth, the NTP list is one-dimensional. It makes no attempt to separate out any possible benefits of the listed chemicals, only their purported cancer risk -- and shockingly, the list makes no reference to dose of exposure as it relates to risk. For example, the NTP lists tamoxifen as a "known carcinogen" because it increases the risk of uterine cancer, but that label may distract people from another fact NTP notes about the drug: it can reduce the rate of new and recurrent breast cancers in high-risk women. Similarly, the NTP is proposing putting steroidal estrogen on its cancer-causing list because hormone replacement and birth control preparations containing the hormone have been associated with endometrial cancer and, to a lesser extent, breast cancer.
"Consumption of alcoholic beverages" makes the "known cause of cancer" list -- but NTP never mentions what dose. How much alcohol is "known" to cause cancer? One glass of wine a day? It is known that moderate alcohol consumption, in the absence of smoking cigarettes, has never been shown to be a risk factor for cancer. Similarly, this year the NTP for the first time lists certain viruses and "grilled meats" as "carcinogens" -- again without explanation. Indeed, sexually-transmitted viruses do appear to be important in the causation of cervical cancer, and there appears to be a correlation between ingestion of charred meats and stomach cancer in
Giving Americans the facts about how they can reduce their cancer risk is a good idea. But Congress should assign that task to cancer epidemiologists, not toxicologists, and should demand that the presentation of risks be relevant, prioritized and set in a scientific context.
Elizabeth M. Whelan is president of the American Council on Science and Health and editor of the book