Carcinogen classification criteria

Under 1990.112(a), a substance is classified as a Category I Potential Carcinogen when scientific evaluation shows it meets one of three conditions in humans or animal tests. Specifically, 1990.112(a) identifies three routes to Category I: human evidence of carcinogenicity (1990.112(a)(1)); positive results in a single mammalian species long-term bioassay that are supported by other scientifically evaluated evidence (concordance) (1990.112(a)(2)); or a positive long-term bioassay in a single species that is adequately conducted and, in appropriate circumstances, does not require concordance (1990.112(a)(3)).

• Use these three specific criteria to determine Category I classification and cite the applicable subsection when documenting the evidence.

Under 1990.112(a), "concordance" means independent supporting evidence that strengthens a positive long-term bioassay result in one species. The regulation lists examples of concordance as positive results from independent testing in the same or other species, positive short-term tests, or tumors induced at injection or implantation sites (1990.112(a)(3)).

• In practice, concordance shows that a single-species tumor result is not an isolated or spurious finding and helps justify Category I classification.

Under 1990.112(b), a substance is a Category II Potential Carcinogen when the substance meets the criteria in 1990.112(a) but the evidence is only “suggestive,” or when it meets 1990.112(a) criteria in a single mammalian species without evidence of concordance. See the two paths in 1990.112(b) and the specific subparagraphs 1990.112(b)(1) and 1990.112(b)(2).

• Category II is used when the scientific evidence is weaker or less consistent than required for Category I.

Yes; a positive result in a single mammalian species can support Category I if there is concordance with other evidence, or in appropriate circumstances if the long-term bioassay is adequately conducted and the Secretary determines concordance is not necessary. See 1990.112(a)(2) and 1990.112(a)(3).

• Practically, you need either supporting concordant data or a demonstrably robust, well-conducted long-term study that the Secretary finds sufficient.

If human evidence demonstrates carcinogenicity, the substance is classified as a Category I Potential Carcinogen under 1990.112(a)(1).

• Human data provide the strongest basis for Category I classification according to the regulation.

If the Secretary determines the evidence meeting 1990.112(a) is only “suggestive,” the substance is classified as a Category II Potential Carcinogen under 1990.112(b)(1).

• "Suggestive" indicates the evidence does not meet the stronger standards required for Category I.

Positive short-term tests can contribute to concordance, but they do not by themselves replace the need for a long-term bioassay in the classification paths described in 1990.112. The regulation expressly lists positive short-term tests as one form of concordance that can support a long-term bioassay result (1990.112(a)(3)).

• In practice, short-term test positives help corroborate long-term tumor findings but should be used alongside the long-term data the regulation requires.

Yes; induction of tumors at injection or implantation sites is explicitly listed as a form of concordance under 1990.112(a)(3), and can strengthen a single-species long-term bioassay result when determining Category I status.

• Such site-specific tumor findings are one of the recognized types of supporting evidence for concordance.

Positive results across multiple species provide strong evidence of carcinogenic potential and support Category I classification by demonstrating concordance as described in 1990.112(a)(3).

• Multiple-species positives reduce uncertainty about species-specific effects and typically weigh in favor of Category I.

Yes; the Secretary may consider evidence and determine an exception to the 1990.112 criteria under the procedures set out in 1990.143, 1990.144, and 1990.145. The introductory text to 1990.112 states these sections govern consideration of evidence that could warrant exceptions.

• Refer to those procedural sections when special evidence or circumstances may justify departing from the standard criteria.

Under 1990.112(a)(3), if a single-species long-term bioassay is adequately conducted, the Secretary may determine that concordance is not necessary in appropriate circumstances and classify the substance as a Category I Potential Carcinogen.

• In practice, this means a high-quality, well-designed long-term study can sometimes stand on its own for Category I, but the determination rests with the Secretary.

If a substance meets the criteria in a single mammalian species without evidence of concordance, it is classified as a Category II Potential Carcinogen under 1990.112(b)(2).

• Category II reflects the need for caution when single-species results lack corroborating evidence.

Conflicting results across species can lead to weaker overall evidence and may result in a "suggestive" finding or a Category II classification under 1990.112(b)(1), because the evidence meeting 1990.112(a) is judged by the Secretary to be only suggestive.

• When studies conflict, document all results and consider whether additional concordant evidence exists before assigning Category I.

Yes; one form of concordance identified by 1990.112(a)(3) is positive results from independent testing in the same or other species, which means corroborating studies conducted separately can strengthen a single-species positive bioassay.

• Independent replication reduces the risk that a single positive study is an anomaly.

Under 1990.112(b)(1), if the Secretary finds evidence is only suggestive, the substance is classified as Category II. A safety manager should treat the substance as a potential carcinogen, document the evidence and uncertainty, and consider precautionary controls or exposure minimization while awaiting more definitive data.

• Actions can include hazard communication, exposure monitoring, engineering controls, and PPE, consistent with the level of uncertainty and applicable OSHA requirements.

Short-term tests can influence classification but are generally used as supporting evidence for concordance under 1990.112(a)(3). If positive short-term tests exist but do not sufficiently corroborate a long-term bioassay or human data, the Secretary may judge the evidence to be only suggestive and place the substance in Category II under 1990.112(b)(1).

• Short-term tests help but usually are not alone decisive for Category I without stronger long-term or human data.

You can read the full criteria for identification, classification, and regulation of potential occupational carcinogens in 1990.112 of OSHA's rules, which includes the Category I and Category II definitions and related clauses.

• Review the linked section for the exact regulatory language and the specific subparagraphs referenced in classification decisions.