SAN FRANCISCO (CN) – Despite blasting some of an epidemiologist’s opinions as "junk science," a federal judge said Wednesday the expert’s "shaky" conclusion that the world's most popular weed killer causes cancer could still advance more than 300 lawsuits against chemical giant Monsanto.
Monsanto is fighting off claims that glyphosate, the active ingredient in its herbicide Roundup, has caused hundreds of farmers and landscapers to develop non-Hodgkins lymphoma. The lawsuits were consolidated in a multidistrict case in San Francisco.
During a week of expert testimony last week, UCLA epidemiologist Dr. Beate Ritz said that a review of more than a dozen case studies led her to conclude "to a reasonable degree of scientific certainty" that glyphosate causes cancer in humans.
During a causation hearing Wednesday, U.S. District Judge Vince Chhabria cast doubt on that conclusion, saying it appears Ritz failed to adjust the numbers in those studies for other factors that might cause cancer, like exposure to pesticides.
"She has reached this conclusion that I do think is dubious that glyphosate is currently causing non-Hodgkin's lymphoma in human beings," Chhabria said. "But is it outside the range of a reasonable scientific conclusion that epidemiologists can draw?"
Chhabria is not tasked with deciding whether Roundup causes cancer, but he must decide if the science underpinning the plaintiffs' claims is reasonable and admissible as evidence in a jury trial.
Monsanto attorney Eric Lasker, of Hollingsworth LLP in Washington, urged the judge to reject Ritz's expert testimony. He said the epidemiologist based her findings on "unadjusted odds ratios" and "confounded data," rather than "scientifically sound conclusions."
Plaintiffs' attorney Aimee Wagstaff, of Argus Wagstaff in Colorado, gave the judge a detailed list of every instance where Ritz referenced the issue of adjusting for other potential causes of cancer in her reports and testimony.
"Our experts did consider confounding," Wagstaff said, referring to outside influences that can affect health studies. "Each one of them considered the unadjusted and adjusted odds ratios."
"Where is her opinion that the fully or properly adjusted odds ratios and confidence intervals show that glyphosate is causing non-Hodgkins lymphoma in people," Chhabria asked.
"She seems to be saying in her rebuttal report that we shouldn't consider these confounders," he said. "If that's what she's saying, she's clearly wrong."
In 2015, the World Health Organization’s International Agency for Research on Cancer (IRAC) concluded that glyphosate is “probably carcinogenic to humans.” But other studies, including a 2017 review by the U.S. Environmental Protection Agency, reached the opposite conclusion.
On Wednesday, Chhabria warned the plaintiffs that reliance on the IRAC study alone is not enough to support their claims that Roundup causes cancer.
The judge said he has a difficult time understanding how any scientist could conclude based on the evidence presented in court last week that glyphosate causes cancer in human beings.
At the same time, Chhabria said he also questions how any legitimate scientist could reach the opposite conclusion.
"It seems to me there's at least a strong argument that the only reasonable conclusion one could draw right now is that we don't know yet," Chhabria said.
Despite his problems with the "shaky" opinions of the plaintiffs' key expert witness, Chhabria suggested that it may be best for a jury, rather than him, to decide whether those conclusions stand up to scrutiny.
"Maybe Dr. Ritz, despite some of the problems with her testimony, is operating within the mainstream of the field," Chhabira said. "Maybe it's up to the jury to buy her presentation."
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