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Monsanto Mouse Study Looms Large in Roundup Cancer Litigation

Scientist grabbing white mouse

A study that Monsanto presented to the U.S. Environmental Protection Agency (EPA) roughly 34 years ago resurfaced this week in the Roundup cancer lawsuit. The study, which analyzed the effects of glyphosate on rodents, could emerge as a vital piece of evidence for the growing number of plaintiffs who are suing Monsanto. Plaintiffs in the litigation allege exposure to Roundup caused them to develop non-Hodgkin lymphoma.

According to Environmental Health News, Roundup cancer attorneys have hired an expert pathologist to analyze the 1983 Monsanto mouse study, believing slides of mouse tissue could help prove that the agrochemical giant covered up known health risks associated with glyphosate. The lawyers plan to introduce the study analysis as evidence during hearings scheduled to begin in Northern California the week of December 11.

Mice Exposed to Glyphosate in 1983 Study Developed Tumors

In 1983, Monsanto published a study on glyphosate entitled “A Chronic Feeding Study of Glyphosate (Roundup Technical) in Mice” with the intention of submitting the research to regulators.

The study was conducted over a two-year period. Researchers used 400 mice divided into groups of 50 males and 50 females. Each group received different dosages of glyphosate, with the exception of the control group, which wasn’t exposed to the chemical.

According to the study, some of the mice that were administered glyphosate doses developed tumors at statistically significant rates. The mice in the control group, on the other hand, did not develop any tumors.

A review of the study in a 1984 memo from EPA toxicologist William Dykstra stated:

“Review of the mouse oncogenicity study indicates that glyphosate is oncogenic, producing renal tubule adenomas, a rare tumor, in a dose-related manner.” (Oncogenic means, causing the development of a tumor or tumors.)

On the surface, the findings and subsequent review by Dykstra appear significant, if not damaging. But Monsanto downplayed the study’s findings by arguing that the tumors were “unrelated to treatment,” and showed false positives. The company sent additional research to EPA in an effort to discount the tumors discovered in the 1983 study.

EPA experts at the time remained unmoved. According to a 1985 memo from EPA statistician and toxicology branch member Herbert Lacayo, a “prudent person would reject the Monsanto assumption that Glyphosate dosing has no effect on kidney tumor production.” Lacayo went on: “Glyphosate is suspect. Monsanto’s argument is unacceptable.”

The same year, eight members of EPA’s toxicology branch shared enough concern with the study’s results to classify glyphosate as a Category C oncogen, meaning a chemical “possibly carcinogenic to humans.”

Monsanto Reacts to EPA’s Classification of Glyphosate

In the month that followed, Monsanto worked to redress the EPA’s kidney tumor concerns. According to an April 3, 1985 memo sent by George Levinskas, Monsanto’s manager for environmental assessment and toxicology, the company arranged for Dr. Marvin Kuschner, founding dean of the medical school at the State University of New York at Stony Brook, to review the 1983 Monsanto mouse study.

Dr. Kuschner hadn’t yet looked at the kidney tumor slides from the study when Levinskas sent the memo. Nonetheless, Levinskas allegedly implied in the memo that Dr. Kuschner’s analysis of the slides would provide the company with a favorable outcome.

Levinskas wrote in the memo:

“Kuschner will review kidney sections and present his evaluation of them to EPA in an effort to persuade the agency that the observed tumors are not related to glyphosate,”

Indeed, when Dr. Kuschner reviewed the study, he determined the kidney tumors were not related to glyphosate. Looking at slides of mouse tissue from the study, Dr. Kuschner found a small kidney tumor among mice that weren’t exposed to glyphosate. The tumor incidence among mice in the control group wasn’t reported in the original study.

Monsanto also provided EPA with a report from a “pathology working group” in October 1985, which further rebutted the connection between glyphosate and kidney tumors. According to this report, which Monsanto stamped as a trade secret to be kept out of public view, “spontaneous chronic renal disease” was “commonly seen in aged mice.” EPA scientists didn’t agree with the reports. Nonetheless, Monsanto’s rebuttal efforts created enough debate to influence the agency to reinvestigate the controversial 1983 mouse study.

In 1986, an EPA scientific advisory panel found that in lieu of the tumors among control group mice found by some pathologists, the data was not statistically significant enough to warrant glyphosate’s Category C designation.

Still, the panel said the Monsanto mouse study was concerning, and that the tumor incidences observed among mice given dosages of glyphosate was “unusual.” The panel said the mouse oncogenicity study should be repeated to produce more definitive findings, but Monsanto refused to repeat the study, arguing there wasn’t any regulatory or scientific justification for further research.

The stalemate between Monsanto and EPA continued for years, as Monsanto continued to claim that repeating the study was unnecessary. In 1989, EPA decided to drop the requirement to repeat the mouse study, despite a number of agency scientists who harbored lingering doubts about the legitimacy of Monsanto’s data.

The significance of the initial Monsanto mouse study declined as time passed. In 1991, when an EPA review committee met to evaluate glyphosate research, the agency determined there was a “lack of convincing carcinogenicity evidence” in relevant animal studies. The committee decided to reclassify glyphosate as a Group E chemical, meaning “evidence of non-carcinogenicity for humans.” At least two committee members refused to sign the reclassification report, saying they didn’t agree with the findings.

Monsanto Mouse Study ‘Extremely Relevant’ to Litigation

According to Roundup cancer attorneys, the 1983 Monsanto mouse study created a chain of events that are now “extremely relevant” to the litigation against Monsanto. Plaintiffs’ attorneys wrote in a recent court filing that the kidney slides from the 1983 study are “immense to the question of general causation and played a critical role in the EPA’s decision to re-categorize glyphosate…”

The 1983 Monsanto mouse study isn’t the only rodent study to find a causal link between glyphosate and cancer. A 1981 study showed exposure to glyphosate carried an increased risk of tumor growth in the testes of male rats and possible thyroid carcinomas among female rats. A 1990 study showed pancreatic tumors among rats exposed to glyphosate.

Christopher Portier, the former director of the National Center for Environmental Health and Agency for Toxic Substances and Disease Registry at the U.S. Centers for Disease Control and Prevention, believes regulators have taken a “scientifically flawed” approach to evaluate glyphosate studies, thus putting public health at risk.

“The data in these studies strongly supports the ability of glyphosate to cause cancer in humans and animals; there is no reason to believe that all of these positive studies arose simply by chance,” says Portier.



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