The federal "cancer scare" machine this week labeled sunlight, birth control pills, hormone replacement therapy, wood dust and 12 other substances as "known" to cause cancer in humans.
These additions bring to 228 the total number of substances supposedly "known" or "reasonably anticipated" to cause cancer.
Department of Health and Human Services Secretary Tommy Thompson says the National Toxicology Program's biennial report on carcinogens "helps all of us ensure that the American public is made aware of potential cancer hazards."
What the American public should be made aware of is the certain absurdity of the NTP's cancer labeling scheme.
First, the notion that substances by themselves cause cancer is faulty. There is not a single substance or group of substances that, acting alone, causes cancer in all people at any and every level of exposure.
Many circumstances affect human cancer risk, including the level and duration of exposure to a substance, and, more importantly, an individual's genetic make-up and lifestyle.
Sure long-term overexposure to sunlight may increase the risk of skin cancer for some people, but the cause-and-effect is obviously not as simple as the wrong-headed conclusion that any exposure to sunlight necessarily leads to skin cancer in everyone -- the face-value implication of the NTP label.
The NTP earlier labeled the anti-miscarriage drug diethylstilbesterol (DES) as "known" to cause cancer. DES was prescribed to millions of American women from 1946 to 1971 and was eventually associated with a rare type of cancer in the daughters of mothers who took DES.
But only about 700 cases of the cancer in DES daughters have been reported worldwide. The DES daughters' lifetime risk of the cancer is estimated to be between one in 1,000 to one in 10,000. Far from definitely "causing" cancer, in fact, DES is unlikely to cause cancer -- except to the NTP.
For the NTP, if a substance may have contributed to cancer development in a small number of individuals, then that substance is deemed a "known" carcinogen. Forget that the substance doesn't cause cancer among the vast majority of people.
It's not even clear that substances labeled as "known" to be cancer-causing have anything to do with cancer development under any circumstances -- examples include hormone replacement therapy, secondhand smoke, soot and PCBs.
In addition to the fundamental silliness of labeling substances as cancer-causing, the NTP process is suspect.
The NTP is government-run and inherently political. The program has seemed overanxious to label industrial chemicals, pesticides, alcoholic beverages and secondhand smoke as cancer-causing.
The NTP apparently views political correctness as a scientific criterion.
To be listed as a "known" cancer-causing substance according to NTP rules, the sole requirement is that, "There must be sufficient evidence of carcinogenic from studies in humans which indicates a causal relationship between exposure to the agent, substance or mixture and human cancer."
This might lead one to expect that the NTP review committee would be chock full of experts in human studies -- that is, trained epidemiologists.
But none of the 13 members of the NTP review committee are epidemiologists by training or renown. They simply aren't professionally qualified to render judgment.
The process for labeling a substance as "reasonably anticipated" to cause cancer is also deeply flawed.
For "reasonably anticipated" to cause cancer, all that's required is "sufficient evidence of [cancer-causing potential] in experimental animals."
But this overlooks the fact that mice simply aren't little people. Just because laboratory mice poisoned with high doses of chemicals have higher rates of cancer doesn't necessarily mean that much lower, more typical exposures are dangerous to humans.
Moreover, laboratory animals are inbred to be prone to cancer development. In effect, they're cancer time bombs. They're so sensitive that even the amount of food they eat significantly affects their cancer risk.
It's no wonder that genetically unstable lab animals develop cancer in experiments where they're administered substances at levels just below what would constitute poisoning.
A notable irony of the current NTP report is that in the same breath sunshine is listed as a "known" carcinogen, the substance methyleugenol -- used in sunscreen -- is labeled as "reasonably known" to cause cancer.
The NTP, it seems, wants us to keep us in the dark.
Steven Milloy is the publisher ofJunkScience.com , an adjunct scholar at the Cato Institute and the author of Junk Science Judo: Self-defense Against Health Scares and Scams (Cato Institute, 2001)
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