Featuring a foreword by Richard A. Williams, Ph.D. Dr. Williams is an expert in benefit-cost and risk analysis. He retired from the Food & Drug Administration after a 27-year career during which he served as Chief Social Scientist at the Center for Food Safety and Applied Nutrition. Dr. Williams also served for nine years as Director of Regulatory Studies at the Mercatus Institute and currently serves on the Board of the non-profit Toxicology Excellence for Risk Assessment.

Executive Summary

The World Health Organization established the International Agency for Research on Cancer (IARC) in 1965 to advance global cancer research, including identifying carcinogenic risks from chemical exposures. Over time, however, its mission evolved toward classifying hazards rather than risks and expanded from studying merely chemicals to reviewing complex exposures (e.g., firefighting, rubber manufacturing) and even lifestyle factors (e.g., nightshift work). The precautionary principle heavily influences IARC’s current classification system, resulting in systematic overstatement of carcinogenic hazards, distortion of scientific evidence, and corrosive downstream impacts on regulation and litigation.

IARC prepares monographs that evaluate agents’ carcinogenicity to humans and then assigns their research targets a hazard classification (Group 1, 2A, 2B, and 3). As discussed in Section I, this classification is based on the strength of evidence that the agents can cause cancer—but not on the likelihood that they do so under real-world conditions. This distinction between “hazard” and “risk” is fundamental but often misunderstood. “Hazard” merely indicates capability, whereas “risk” requires quantification of exposure and probability. IARC’s failure to clearly communicate this distinction has led regulators, courts, and the public to treat hazard classifications as evidence of real-world danger, thereby amplifying fear and misunderstanding.

Sections II and III highlight the semantic distortions embedded in IARC’s methodology. Terms such as “probably carcinogenic” (Group 2A) and “possibly carcinogenic” (Group 2B) do not carry quantitative meaning, contrary to their common interpretation. In practice, “probably” may reflect very low levels of certainty, far below the legal threshold of “more likely than not.” In addition, the evidentiary standards required to classify an agent as carcinogenic are significantly lower than those required to conclude lack of carcinogenicity. Further, IARC’s reliance on human epidemiology, animal studies, and mechanistic data for evidence—integrated through subjective algorithms and decision trees—leads to cherry-picking of studies and inconsistent handling of conflicting data.

Sections IV – VI examine three IARC institutional flaws that empower precaution proponents. The first concern assessed is IARC’s departure from modern standards for systematic reviews. The agency utilizes some of the review methods the scientific community considers essential, but does not require pre-registered protocols, structured bias assessment tools, or external peer review. IARC working groups operate with broad discretion, often without transparent criteria for study inclusion, exclusion, or weighting.

Second, IARC’s approach to conflicts of interest is inconsistent and characterized by a single-minded goal of excluding anyone with industry ties. As a result, individuals affiliated with environmental advocacy groups, litigation interests, or precaution-oriented scientific groups like the Collegium Ramazzini dominate IARC working groups. IARC’s anti-industry bias and failure to police ideological, professional, or publishing conflicts has tainted categorization efforts for agents like electromagnetic fields and glyphosate.

Third, despite its asserted adherence to transparency, IARC’s procedures and deliberative process are largely opaque. Working group deliberations are confidential, voting records are undisclosed, draft materials are not publicly accessible, and, as noted previously, reports are not subject to public peer review. This dynamic further entrenches precautionary bias and groupthink, both of which undermine objective scientific inquiry.

Sections VII and VIII explore how IARC’s methodological and governance shortcomings have far-reaching consequences on civil litigation and government regulation. The Federal Judicial Center’s Reference Manual on Scientific Evidence accords IARC and its monographs undeserved accolades and inaccurately states that federal courts generally recognize monographs as “authoritative.” IARC classifications frequently serve as a basis for mass tort claims despite lacking direct evidence of causation. Mr. Schachtman refers to this phenomenon as “tortogenesis,” whereby classifications effectively generate lawsuits. The classifications also influence regulatory frameworks, particularly in jurisdictions like California under Proposition 65, where hazard classifications trigger warning requirements regardless of actual exposure risk.

IARC’s monograph program has become outdated, redundant, and counterproductive. Advances in systematic review methodologies and the availability of high-quality, transparent evidence synthesis by national and international bodies have diminished the need for IARC’s approach. Moreover, the secrecy of its processes and the lack of accountability contrast sharply with modern standards of scientific and regulatory governance.

Mr. Schachtman recommends that U.S. regulatory officials and the judiciary reconsider reliance on IARC classifications in regulatory and legal contexts, demand IARC increase transparency and methodological rigor, and potentially withdraw financial and institutional support for the monograph program. At a minimum, Mr. Schachtman urges policymakers and judges to understand that precautionary conclusions like those resulting from IARC monograph projects are policy choices and should not be confused with scientific conclusions.

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