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The BCERF program on the Cancer Risks of Environmental Chemicals in the Home and Workplace closed on March 31, 2010. No further updates will be made to this web site. Please go Cornell University’s eCommons web site to access BCERF’s archived research and educational materials (http://ecommons.library.cornell.edu/handle/1813/14300).

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Critical Evaluation:
2, 4-D
Fact Sheet: 2, 4-D
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BCERF Breast Cancer Risk Classification Scheme

Adapted Cancer Risk Classification Scheme
BCERF's translational research on selected pesticides and their cancer risk is compiled into monograph style technical reports called Critical Evaluations. In preparing the evaluations, BCERF uses a cancer risk classification scheme adapted from the International Agency for Research on Cancer (IARC) preamble.

Cancer Classification Groupings

Group 1: Human breast carcinogen
Sufficient evidence of breast carcinogenicity in human studies is necessary for an agent to be classified as a human breast carcinogen. Sufficient evidence is considered to be evidence that a causal relationship has been established between exposure to the agent and human breast cancer.

Group 2A: Probable breast carcinogen
This category generally includes agents for which there is: 1.) limited evidence of breast carcinogenicity in humans and sufficient evidence of mammary carcinogenicity in experimental animals. The classification may also be used when there is: 2.) limited evidence of breast carcinogenicity in humans and strong supporting evidence from other relevant data, or when there is: 3.) sufficient evidence of mammary carcinogenicity in experimental animals and strong supporting evidence from other relevant data.

Group 2B: Possible breast carcinogen
This category generally includes agents for which there is: 1.) limited evidence of breast carcinogenicity in humans in the absence of sufficient evidence of mammary cancer in experimental animals; 2) inadequate evidence of breast carcinogenicity in humans or when human data are nonexistent but there is sufficient evidence of mammary carcinogenicity in experimental animals, or 3) inadequate evidence or no data in humans but with limited evidence of mammary carcinogenicity in experimental animals together with supporting evidence from other relevant data.

Group 2C: Potential to affect breast cancer risk
This category includes agents for which there is inadequate or nonexistent human and animal data, but there is supporting evidence from other relevant data that identifies a mechanism by which the agent may affect breast cancer risk. Examples are, but are not limited to: evidence of agent's estrogenicity, disruption of estrogen metabolism resulting in potential to affect exposure to estrogen; evidence of breast tumor promotion, progression or co-carcinogenicity; increased expression of proto-oncogenes or oncogenes; evidence of inactivation of tumor suppressor gene associated with breast cancer; evidence of adverse affect on immune function that would affect breast cancer risk; or evidence of a structural similarity to a known breast carcinogen (structure-activity relationship).

Group 3: Not classifiable as to its breast carcinogenicity
Agents are placed in this category when they do not fall into any other group. This includes agents where there is inadequate evidence for breast carcinogenicity in human, animal, or related studies but the studies conducted have not established that the agents have no breast cancer risk (the absence of studies does not constitute evidence for a lack of breast carcinogenicity). Agents are also placed in this category if there is evidence of carcinogenicity at other non-breast-sites in experimental animal studies, since there is not always complete concordance between the sites of tumors in animals and humans.

Group 4: Probably not a breast carcinogen in humans
This category is used for agents for which there is evidence demonstrating a lack of breast carcinogenicity in human studies and in animal studies, together with a lack of related evidence which may predict breast cancer risk. The absence of studies does not constitute evidence for a lack of breast carcinogenicity.

Brief Definitions of Strength of Evidence Terminology

Human Studies

Sufficient Evidence of breast carcinogenicity in humans
Must have established evidence between exposure to the agent and human breast cancer. Case reports are given the least weight in considering breast carcinogenicity data in humans - they are suggestive of a relationship, but by themselves cannot demonstrate causality. Consistent results from case-control studies and/or nested case-control studies which have controlled for confounding factors and have found high relative risks of developing breast cancer in relation to an identified exposure; these are given the most weight in determining a causal relationship.
Limited evidence of breast carcinogenicity in humans
A positive association has been observed between exposure to the agent and breast cancer, but chance, bias, or confounding factors could not be ruled out.
Inadequate evidence of breast carcinogenicity in humans
The available studies are of insufficient quality, consistency, or statistical power to permit a conclusion regarding the presence or absence of a causal association.

Experimental Animal Studies

Sufficient evidence of breast carcinogenicity in animals
Evidence of malignant tumors or combination of benign and malignant tumors in (a) two or more species of animals, (b) or two or more independent studies in one species carried out at different times or in different laboratories or under different protocols.
Limited evidence of breast carcinogenicity in animals
The studies suggest a carcinogenic effect, but are limited for making a definitive evaluation because: (a) the evidence of carcinogenicity is restricted to a single experiment; (b) there are unresolved questions regarding the adequacy of the design, conduct, or interpretation of the study; or (c) the agent increases the incidence of only benign neoplasms of lesions of uncertain neoplastic potential, or of certain neoplasms which may occur spontaneously in high incidences in certain strains of animals.
Inadequate evidence of breast carcinogenicity in animals
The studies cannot be interpreted as showing either the presence or absence of a carcinogenic effect because of major qualitative or quantitative limitations.