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Ethylene Oxide: Cancer Evidence Integration and Dose-Response Implications
Melissa J Vincent1, Jordan S Kozal2, William J Thompson3
1Cardno ChemRisk, Cincinnati, OH, USA.
Dose-Response : a Publication of International Hormesis Society
|December 20, 2019
Summary
Ethylene oxide (EtO) is classified as a carcinogen, but this review finds limited human evidence for breast and lymphoid cancers. Animal data and risk assessments may overestimate EtO
Area of Science:
- Environmental Health
- Toxicology
- Epidemiology
Background:
- The International Agency for Research on Cancer (IARC) and the United States Environmental Protection Agency (USEPA) classify ethylene oxide (EtO) as a known human carcinogen.
- Classifications rely on limited human epidemiological data for lymphoid and breast cancers, alongside sufficient/extensive animal study data and genotoxicity findings.
- The USEPA established a high inhalation unit risk (IUR) for EtO based on two epidemiological studies.
Purpose of the Study:
- To critically review the epidemiological and toxicological evidence for ethylene oxide (EtO) carcinogenicity.
- To evaluate the USEPA's reliance on a genotoxic mode of action for EtO carcinogenicity and dose-response assessment.
- To reassess the accuracy of EtO's classification and the derived inhalation unit risk (IUR).
Main Methods:
- Focused review of epidemiological studies on EtO and cancer risk, particularly breast and lymphohematopoietic malignancies (LHM).
- Focused review of toxicological studies and biomarker data in animals and humans related to EtO exposure.
- Analysis of the USEPA's methodology for establishing EtO's carcinogenicity and dose-response relationships, including its genotoxic mode of action assumption.
Main Results:
- Higher-quality epidemiological studies showed no increased risk for breast cancers or lymphohematopoietic malignancies (LHM).
- Toxicological and biomarker studies provided weak evidence linking EtO to LHM or mammary cancers in animals and humans.
- Animal data were insufficient to confidently determine dose-response curves or predict tumor risks at low EtO doses.
Conclusions:
- The classification of ethylene oxide (EtO) as a known human carcinogen by IARC and USEPA appears to overstate the available evidence.
- The inhalation unit risk (IUR) calculated by the USEPA likely overestimates the actual cancer risk associated with EtO exposure.
- Re-evaluation of EtO's carcinogenic potential and risk assessment is warranted based on a comprehensive review of human and animal data.
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