The widely used herbicide Roundup, containing the active ingredient glyphosate, has prompted questions about its potential long-term health effects, particularly concerning cancer. Glyphosate-based products are applied globally in agriculture, forestry, and consumer settings for broad-spectrum weed control, leading to widespread human exposure. The most specific question is whether exposure to this herbicide is linked to the development of Acute Myeloid Leukemia (AML), a severe form of blood cancer. This article examines the current scientific evidence, regulatory positions, and the status of legal claims focused on the alleged connection between glyphosate and AML.
What is Acute Myeloid Leukemia and Glyphosate
Glyphosate is an organophosphorus compound and the active chemical component in the herbicide Roundup, first introduced commercially in 1974. It functions as a broad-spectrum, non-selective systemic weed killer by inhibiting a specific enzyme pathway necessary for plant growth. The chemical is used globally to manage weeds in agricultural fields, often with genetically modified crops, and in non-agricultural settings like residential lawns and parks.
Acute Myeloid Leukemia (AML) is a rapidly progressing cancer of the blood and bone marrow. It is characterized by the uncontrolled growth of abnormal white blood cells called myeloblasts. These abnormal cells accumulate and crowd out the production of healthy blood components, leading to a rapid onset of symptoms like fatigue and recurrent infections. AML is considered an aggressive disease that requires immediate and intensive treatment, distinguishing it from slower-growing, chronic leukemias.
Specific Scientific Findings on the AML Link
Scientific investigation into the connection between glyphosate and AML has yielded results that are largely inconclusive on a population level. The most frequently cited human epidemiological data comes from the Agricultural Health Study (AHS), a large, long-term prospective cohort study of licensed pesticide applicators in the U.S. An update to the AHS found no statistically significant association between glyphosate use and overall cancer risk, including Non-Hodgkin Lymphoma (NHL).
However, the same AHS update did report a potential signal specifically for AML among the highest-exposed applicators compared to those who had never used the product. The risk ratio for AML in the highest exposure quartile was elevated, but the finding was not statistically significant, meaning researchers cannot definitively rule out that the result was due to chance. The study authors concluded that the increased risk suggested by the data warranted confirmation through additional research.
Beyond human epidemiology, toxicological studies in animals have explored the potential for glyphosate to cause leukemia. A long-term study conducted by the Ramazzini Institute exposed rats to low doses of glyphosate and glyphosate-based formulations, starting during the prenatal period. This study reported a dose-dependent increase in benign and malignant tumors, with leukemia being observed earlier and more frequently in the treated animals. These animal findings suggest a theoretical biological mechanism related to the chemical’s potential to cause genotoxicity, or damage to the cell’s genetic material, which is a known pathway to blood cancers.
Regulatory Determinations and Risk Assessment
Major governmental and international health organizations have reached different conclusions regarding the overall cancer risk of glyphosate. The U.S. Environmental Protection Agency (EPA) has consistently concluded that glyphosate is “not likely to be carcinogenic to humans.” This conclusion is based on a comprehensive review of epidemiological, animal carcinogenicity, and genotoxicity studies. The EPA’s assessment found no human health risks of concern when the product is used according to its label directions.
In contrast, the International Agency for Research on Cancer (IARC), an arm of the World Health Organization, classified glyphosate in 2015 as “probably carcinogenic to humans” (Group 2A). This hazard classification was based on limited evidence of cancer in humans, primarily non-Hodgkin lymphoma, and sufficient evidence in experimental animals. IARC’s determination is a hazard classification, meaning it assesses the potential for a substance to cause cancer under any circumstances, not the actual risk level posed by typical use.
The differing conclusions between the EPA and IARC stem from the distinct nature of their assessments. The EPA performs a risk assessment, considering real-world exposure levels and finding no risk for AML or other cancers. IARC’s hazard assessment focuses on the strength of the evidence that a chemical can cause cancer, regardless of the exposure level.
Status of Legal Claims Related to AML
The legal landscape surrounding Roundup and cancer has been active, with some claims specifically citing AML. The majority of high-profile litigation has focused on Non-Hodgkin Lymphoma, where stronger epidemiological evidence exists. However, plaintiffs diagnosed with AML after exposure to glyphosate-based products have also filed lawsuits.
These legal claims assert that the manufacturer failed to warn users about the potential carcinogenic risks of the herbicide, including the risk of developing AML. Proving a specific case of AML causation in court presents a unique hurdle for plaintiffs due to the lack of a clear, statistically significant link in large-scale human epidemiological studies. The legal standard of proof for causation in a courtroom is often different from the scientific standard required for a broad health conclusion.
The legal status of these AML claims remains part of the broader, ongoing multidistrict litigation concerning glyphosate and blood cancers. Successful legal outcomes often rely on expert testimony and internal company documents to establish that the manufacturer knew or should have known about a potential cancer risk.