Environment and Breast Cancer: Science Review
« Place cursor over headings for an explanation of data.
The list(s) or database(s) in which the chemical was identified as showing an increase in mammary gland tumors. CPDB: Carcinogenic Potency Database, IARC: International Agency for Research on Chemicals Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man summaries, NTP TR: National Toxicology Program (NTP) Technical Reports, NTP 11ROC: NTP 11th Report on Carcinogens, CCRIS: Chemical Carcinogenesis Research Information Service.Carcinogenicity Potency Database, IARC Monographs, Chemical Carcinogenesis Research Information System
Image from the National Library of Medicine
Names of closely related chemicals discussed in the "originating list" are listed here if they were not separately reviewed.none
We assigned each chemical into one of the following groups based on its major sources and uses: industrial chemicals, chlorinated solvents, products of combustion, pesticides, dyes, radiation and drinking water disinfection, pharmaceuticals, hormones, natural products, and research chemicals.Drinking water disinfection byproduct
If a chemical is a High Production Volume chemical, added to food, found in air pollution or consumer products, or causes greater than 5000 women to be exposed occupationally, it was judged to cause a likely widespread exposure to women in the United States.More Likely
Human exposure summary
Information describing pathways of exposure for the general population was obtained from a variety of sources, including IARC Monographs (9), NTP 11th ROC (4), NTP Study Reports (3), and Hazardous Substance Database (10). Summaries of chemical use in consumer products were developed from information found in US EPA's Source Ranking Database (SRD) (11), the NLM Household Product Database (HPD)(12), Scorecard (12), and Pesticide Action Network (PAN) Pesticides Database (13). If a chemical could not be found in these sources, we searched ToxNet (14), PubChem (15), and The Merck Index (16), and conducted searches by both name and CAS No. using Google.By-product of drinking water disinfection that has been found at nanogram-per-litre levels in drinking water as a result of chlorination or chloramination (IARC 2004 vol.:84 p.441). General population may be exposed via treated (chlorinated) drinking water.
Mammary gland tumor summary
A summary of findings related to mammary gland tumors, most often excerpted from IARC Monographs or the NTP 11th ROC, and, in some cases, supplemented by our evaluation of individual studies and reviews, is available for the priority chemicals and 67 others.Only one study on MX exists and it reports a statistically significant trend of mammary tumors with increased dose.
Risk assessment summary
For 11 chemicals that are of particular interest because of recent regulatory attention, a Silent Spring Institute summary of how the evidence on mammary gland tumors and the potential for breast cancer was considered in major governmental risk assessments and regulations is available.MX is a mutagenic compound formed during disinfection of drinking water. It has been identified as the major contributor to mutagenicity of chlorinated drinking water (1). Many potentially carcinogenic chemicals are formed during the disinfection process, and many studies have been conducted to describe potential risks. Increased risk of breast cancer has been observed in a few epidemiologic studies, but other cancers (e.g. bladder) have been the focus of this work. MX is the only identified disinfection by-product (DBP) that has been shown to increase mammary gland tumors in animal studies, but many DBPs have not yet been chemically identified or tested. Higher levels of DBPs are formed by chlorination of water polluted with sewage and other organic waste, and the most effective method for reducing levels of DBPs is protection of water quality in the source water (2). US EPA does not mention breast cancer or mammary gland tumors in its most recent regulation pertaining to DBPs; this regulatory risk assessment estimates that between 2 and 17% of all bladder cancers in the US are due to DBPs (3). References
International Agency for Research on Cancer evaluation
Overall evaluation: Group 1: The agent is carcinogenic to humans. Group 2A: The agent is probably carcinogenic to humans. Group 2B: The agent is possibly carcinogenic to humans. Group 3: The agent is not classifiable as to carcinogenicity in humans. Group 4: The agent is probably not carcinogenic to humans. NA: not evaluated by IARC (9).2B: Possibly carcinogenic to humans
Evidence in humans
Strength of the evidence in humans (summary of epidemiologic evidence) and animals: sufficient, limited, or inadequate. If IARC has not reviewed the chemical, this field will be labeled "NA".inadequate
Tumor sites identified in IARC Monographs
If tumors were found in humans, the entry in this field will be labeled "(human)." Unlabeled terms are from animal studies. Tumor sites are abbreviated and can be referenced in the key (Table 1). NA: not evaluated by IARC.thyroid, mammary gland (one study, but potent mutagen)
Evidence in animals
Strength of the evidence in humans (summary of epidemiologic evidence) and animals: sufficient, limited, or inadequate. If IARC has not reviewed the chemical, this field will be labeled "NA".limited
US EPA cancer classification
The US EPA Weight of Evidence Characterization of the chemical’s carcinogenic potential is listed: Group A: Carcinogenic to humans; Group B: Probably carcinogenic to humans. Group C: Possibly carcinogenic to humans. Group D: Not classifiable as to human carcinogenicity. Group E: Evidence of non-carcinogenicity for humans. NA: Not evaluated by US EPA (17).NA
National Toxicology Program Study Conclusions
The National Toxicology Program Technical Reports include a determination of the carcinogenicity of the test chemical in each sex and species tested. Designations prior to 1983 are "positive" or "negative". After 1983, NTP assigned designations of "clear evidence of carcinogenicity," "some evidence of carcinogenicity," "equivocal evidence of carcinogenicity," "no evidence of carcinogenicity," or "inadequate study of carcinogenicity." The words "of carcinogenicity” are removed from the field in this database to conserve space. "NA" indicates no NTP technical report for the chemical (3).
Mutagenicity from CPDB
This summary of evidence from the Carcinogenic Potency Database is labeled “Yes” if the agent is mutagenic or weakly mutagenic in the Salmonella assay and “No” if not. NA: Not listed in CPDB. NA-S: Listed in CPDB, but no assessment of mutagenicity in Salmonella is included (1).NA-S
Mutagenicity from RTECS
This summary of evidence from the Registry of Toxic Effects of Chemical Substances database (NIOSH 2005) is labeled “Yes” if the agent is listed as mutagenic, “No” if not. NA: Not listed in RTECS (18).Mutagenic