In March 2015, the International Agency for Research on Cancer (IARC) classified glyphosate—the most commonly used herbicide worldwide—as Group 2A “probably carcinogenic to humans.” That classification prompted the filing of litigation against Monsanto, claiming that glyphosate—the active ingredient in Monsanto’s Roundup herbicide—caused numerous plaintiffs to develop non-Hodgkin’s lymphoma (NHL). This highly publicized litigation currently involves hundreds of cases that are consolidated in MDL No. 2741 before Judge Vince Chhabria in the Northern District of California, and thousands of additional cases in state courts in California, Delaware, and Missouri.
Not surprisingly, causation is a critical and hotly disputed issue in the litigation. The plaintiffs’ experts opine that in vivo animal studies, case-control epidemiology studies and genotoxic studies evidence an etiological link between glyphosate exposure and NHL. Monsanto’s experts rebuff that alleged causal connection based on cohort epidemiology studies finding no association between glyphosate and NHL, and by challenging the significance and reliability of plaintiffs’ experts’ studies. In this dispute, Monsanto cites to the testimony of plaintiffs’ experts that existing epidemiological data is “not sufficient to show a causal relationship between glyphosate and non-Hodgkin’s lymphoma,” and emphasizes the lack of any epidemiology showing a statistically significant association between glyphosate exposure and NHL. On these and other grounds, Monsanto has challenged the admissibility of plaintiffs’ experts’ opinions under Daubert in a motion filed on October 6, 2017, which was scheduled to be heard in December 2017.
Gatecrashing that Daubert dispute, scientists from the National Cancer Institute and National Institutes of Health handed Monsanto what they argue is “the most powerful scientific evidence that now exists regarding [glyphosate-based herbicides] and NHL.” The study—"Glyphosate Use and Cancer Incidence in the Agricultural Health Study”—is an independent study published in the Journal of the National Cancer Institute on November 9, 2017 (the 2017 AHS Study), which Monsanto asserts was performed without any involvement or funding by Monsanto. The study involved a prospective cohort of 54,251 licensed pesticide applicators who enrolled in the study between 1993 and 1997, of whom 44,932 (82.8 percent) used glyphosate. The study found no statistically significant increased risk of NHL in users of glyphosate compared to nonusers and therefore concluded that “no association was apparent between glyphosate and . . . NHL and its subtypes.” Monsanto argues that “[t]he 2017 AHS study is by far the largest epidemiological study of the potential association between [glyphosate-based herbicides] and NHL,” and “the significance of the 2017 AHS Study on the Court’s Daubert inquiry into plaintiffs’ experts’ causation opinions cannot be overstated.” In Re: Roundup Products Liability Litigation, 3:16-md-02741-VC, Dkt. 697.
The plaintiffs disagree. They concede the 2017 AHS Study “shows no association” between glyphosate use and non-Hodgkin’s lymphoma. Id., Dkt. 698. In this regard, the plaintiffs’ say that the 2017 AHS Study “is not ‘new,’” claiming it is merely an updated version of prior studies which also “show no positive association between glyphosate use and non-hodgkins lymphoma (NHL).” [sic] Id. However, they argue the 2017 AHS Study, like prior studies, has “numerous methodological flaws.” Id. The principal flaw asserted is the study’s “misclassification of exposure, i.e. miscategorizing participants as exposed to or unexposed to glyphosate, which was exacerbated by not properly accounting for the dramatic increase in Roundup use on genetically modified crops after they entered the market in 1996.” Id. The plaintiffs argue that the questioning and the cohort’s participation rate in follow-up interviews created a gap in knowledge of cohort members’ use of glyphosate during “the time period when exposures to glyphosate skyrocketed.” Id. The plaintiffs argue that this gap in knowledge yielded “irrelevant and unreliable results,” and makes the 2017 AHS Study “methodologically flawed because there is no adjustment for the significant increased use of glyphosate during the years of imputation.” Id.
Despite the plaintiffs’ arguments, Judge Chhabria continued the December 2017 hearing dates for expert testimony and lawyer argument on Monsanto’s Daubert motion until March 2018, to allow further consideration of the 2017 AHS Study through additional discovery and briefing about it. Thus, with the plaintiffs’ claims hanging in the balance, this massive cohort epidemiology study is now the proverbial “elephant in the room” for the plaintiffs, which will challenge the plaintiffs’ experts’ causation methodologies and opinions in the proceeding. However, whether it is enough to dispose of the plaintiffs’ claims under Daubert will have to be seen.