The Mythology of Linear No-Threshold Cancer Causation

“For the great enemy of the truth is very often not the lie—deliberate, contrived, and dishonest—but the myth—persistent, persuasive, and unrealistic. Too often we hold fast to the clichés of our forebears. We subject all facts to a prefabricated set of interpretations. We enjoy the comfort of opinion without the discomfort of thought.”

John F. Kennedy, Yale University Commencement (June 11, 1962)

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The linear no-threshold model for risk assessment has its origins in a dubious attempt of scientists playing at policy making[1]. The model has survived as a political strategy to inject the precautionary principle into regulatory decision making, but it has turned into a malignant myth in litigation over low-dose exposures to putative carcinogens. Ignorance or uncertainty about low-dose exposures is turned into an affirmative opinion that the low-dose exposures are actually causative. Call it contrived, or dishonest, or call it a myth, the LNT model is an intellectual cliché.

The LNT cliché pervades American media as well as courtrooms. Earlier this week, the New York Times provided a lovely example of the myth taking center stage, without explanation or justification. Lumber Liquidators is under regulatory and litigation attack for having sold Chinese laminate wood flooring made with formaldehyde-containing materials. According to a “60 Minutes” investigation, the flooring off-gases formaldehyde at concentrations in excess of regulatory permissible levels. See Aaron M. Kessler & Rachel Abrams, “Homeowners Try to Assess Risks From Chemical in Floors,” New York Times (Mar. 10, 2015).

The Times reporters, in discussing whether a risk exists to people who live in houses and apartments with the Lumber Liquidators flooring sought out and quoted the opinion of Marilyn Howarth:

“Any exposure to a carcinogen can increase your risk of cancer,” said Marilyn Howarth, a toxicologist at the University of Pennsylvania’s Perelman School of Medicine.

Id. Dr. Howarth, however, is not a toxicologist; she is an occupational and environmental physician, and serves as the Director of Occupational and Environmental Consultation Services at the Hospital of the University of Pennsylvania. She is also an adjunct associate professor of emergency medicine, and the Director, of the Community Outreach and Engagement Core, Center of Excellence in Environmental Toxicology, at the University of Pennsylvania Perelman School of Medicine. Without detracting from Dr. Howarth’s fine credentials, the New York Times reporters might have noticed that Dr. Howarth’s publications are primarily on latex allergies, and not on the issue of the effect of low-dose exposure to carcinogens.

The point is not to diminish Dr. Howarth’s accomplishments, but to criticize the Times reporters for seeking out an opinion of a physician whose expertise is not well matched to the question they raise about risks, and then to publish that opinion even though it is demonstrably wrong. Clearly, there are some carcinogens, and perhaps all, that do not increase risk at “any exposure.” Consider ethanol, which is known to cause cancer of the larynx, liver, female breast, and perhaps other organs[2]. Despite known causation, no one would assert that “any exposure” to alcohol-containing food and drink increases the risk of these cancers. And the same could be said for most, if not all, carcinogens. The human body has defense mechanisms to carcinogens, including DNA repair mechanisms and programmed cell suicide, which work to prevent carcinogenesis from low-dose exposures.

The no threshold hypothesis is really at best an hypothesis, with affirmative evidence showing that the hypothesis should be rejected for some cancers[3]. The factual status of LNT is a myth; it is an opinion, and a poorly supported opinion at that.

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“There are, in fact, two things: science and opinion. The former brings knowledge, the latter ignorance.”

Hippocrates of Cos


[1] See Edward J. Calabrese, “Cancer risk assessment foundation unraveling: New historical evidence reveals that the US National Academy of Sciences (US NAS), Biological Effects of Atomic Radiation (BEAR) Committee Genetics Panel falsified the research record to promote acceptance of the LNT,” 89 Arch. Toxicol. 649 (2015); Edward J. Calabrese & Michael K. O’Connor, “Estimating Risk of Low Radiation Doses – A Critical Review of the BEIR VII Report and its Use of the Linear No-Threshold (LNT) Hypothesis,” 182 Radiation Research 463 (2014); Edward J. Calabrese, “Origin of the linearity no threshold (LNT) dose–response concept,” 87 Arch. Toxicol. 1621 (2013); Edward J. Calabrese, “The road to linearity at low doses became the basis for carcinogen risk assessment,” 83 Arch. Toxicol. 203 (2009).

[2] See, e.g., IARC Monographs on the Evaluation of Carcinogenic Risks to Humans – Alcohol Consumption and Ethyl Carbamate; volume 96 (2010).

[3] See, e.g., Jerry M. Cuttler, “Commentary on Fukushima and Beneficial Effects of Low Radiation,” 11 Dose-Response 432 (2013); Jerry M. Cuttler, “Remedy for Radiation Fear – Discard the Politicized Science,” 12 Dose Response 170 (2014).

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