The discussion around glyphosate, a widely used herbicide, is becoming increasingly charged, especially with new studies surfacing that suggest a potential link to cancer. One such study from the Ramazzini Institute (Panzacchi et al 2025) has caught attention for its claims regarding the effects of glyphosate on Sprague-Dawley rats. While the findings indicate a rise in leukemia among the treated rats, a closer examination reveals some nuances that warrant attention.
What are Sprague-Dawley Rats Anyway?
Sprague-Dawley rats are a common choice in scientific research, particularly in toxicology and cancer studies, due to their calm demeanor and consistent performance in experiments. However, the findings from the Ramazzini study prompt us to reflect on how these rats have been used in research historically. A notable example is the Seralini et al. (2012) study, which gained significant media attention, complete with a book launch and press conference, as it claimed to link genetically modified organisms (GMOs) and glyphosate to cancer.
A key aspect that made a huge splash was the striking image of the white rats with numerous tumors. However, this picture raised important questions, particularly because it did not include control rats—likely because the control rats also had tumors. This highlights a critical issue with the Sprague-Dawley strain, which is known for its high rate of spontaneous tumors. The sensationalized findings of the Seralini study were later retracted due to methodological issues, yet the original (retracted) journal article continues to be cited to this day. This connection to the Ramazzini study underscores the need for caution when interpreting research involving this strain of rats.
Rats and Revelations: What the Study Uncovered
The Ramazzini Institute reported a “notable” increase in leukemia cases among rats exposed to glyphosate, while control groups – those not treated with the herbicide – showed no cases at all. At first glance, this seems alarming. However, the absence of leukemia in the control rats contradicts historical data indicating that these rats often develop spontaneous tumors – by design. This raises questions about the interpretation of the results and whether the significance of the treatment groups might be overstated.
The study found that the number of tumors in rats treated with glyphosate and glyphosate-based formulations was pretty low, with leukemia showing up in just 1.96% of the cases. This figure matches what we’ve seen in past research on spontaneous tumors. Interestingly, none of the control rats developed leukemia, which is different from what other studies have reported. The absence of a clear link between the dose of glyphosate and tumor development adds even more uncertainty to the study’s conclusions.
Another point of concern is that the study’s design does not fully adhere to international guidelines for carcinogenicity studies. For example, the survival rates of the rats fell below 50%, which is contrary to recommendations from the Organisation for Economic Co-operation and Development (OECD). This invites one to consider how the study was conducted and whether it was set up to provide reliable insights.
Behind the Scenes: Methods, Ethics, and Rat Tales
The methodology employed in this research has faced scrutiny, particularly regarding its long-term implications. When studies seem to prioritize headlines over rigorous scientific inquiry, it can detract from our collective understanding of critical issues. The quest for attention can sometimes overshadow the pursuit of genuine knowledge.
Additionally, the study appears to favor literature that supports its conclusions while overlooking studies that might present a different perspective. This selective approach can raise eyebrows and lead to questions about the overall integrity of the research.
Related on the SLP
Ramazzini — The backstory of the ‘independent’ Italian organization that partners with IARC, the multi-billion dollar ‘toxic predatort’ industry, and anti-chemical environmental groups
Viewpoint: ‘Travesty of science’: Latest ‘global glyphosate study’ is a scientific mess issued by the ethically-compromised Ramazzini Institute
There are also inconsistencies in reporting initial body weights and water consumption, which could introduce bias into the findings. The absence of detailed pathology reports and tumor evaluations further complicates our ability to assess the biological relevance of the results.
Moreover, the ethical considerations surrounding the treatment of the rats and adherence to established guidelines for prenatal dosing and carcinogenicity testing should not be overlooked. Ensuring ethical standards in animal research is crucial for maintaining public trust in scientific inquiry.
What Do Regulatory Bodies Say?
On a broader scale, regulatory agencies like the U.S. Environmental Protection Agency (EPA) and others around the world (including Health Canada) have concluded that glyphosate does not pose a cancer risk to humans, based on comprehensive reviews of scientific studies. This perspective highlights the importance of a balanced view in the ongoing debate surrounding glyphosate.
Conclusion: A Thoughtful Approach to Science
In summary, the study by Panzacchi et al. (2025) presents significant methodological challenges, particularly regarding its control data and study design. The findings seem to diverge from historical data on spontaneous tumor rates in Sprague-Dawley rats, and the research has faced scrutiny for its selective use of literature and ethical considerations.
As we navigate this complex conversation, it’s vital to approach the topic with a critical yet open mind. The evidence from this study does not definitively support the claim that glyphosate and GBHs are carcinogenic. Let’s continue the dialogue, ensuring that it is grounded in integrity and a commitment to sound scientific principles.
Cami Ryan is a social and behavioral scientist working in agriculture at Bayer CropScience. Follow her on X @CamiDRyan.
A version of this article was originally posted on Substack and is reposted here with permission.
