SAN DIEGO (Legal Newsline) - There’s no need for expert witnesses to point to a specific study showing a substance causes a disease as long as they have a reasonable basis for believing the two are connected, a California appeals court ruled, reversing a trial judge’s disqualification of experts who linked diesel exhaust to blood cancer.
The decision by California’s Fourth District Court of Appeal essentially flips the burden of proof, from requiring plaintiff experts to show published studies supporting their opinions to requiring the defendant to prove experts have no such evidence.
Gary Garner sued BNSF Railway after his father Melvin died of non-Hodgkin’s lymphoma, a common blood cancer associated with aging. Garner claimed his father died after a 40-year career as a trainman where he was exposed to diesel exhaust, benzene, rock dust, asbestos and other carcinogens.
A trial court dismissed Garner’s case after excluding three expert witnesses who offered opinions that diesel exhaust more likely than not caused his father’s non-Hodgkin’s lymphoma. The experts - Drs. Andrew Salmon, Joseph Landolph and Robert Gale - all relied upon studies showing links between diesel exhaust and other cancers, but not specifically non-Hodgkin’s lymphoma.
Garner appealed and the Fourth District reversed, in a Jan. 4 opinion by Judge Martin Buchanan.
The appeals court called it a “misunderstanding of the law” to require expert witnesses to point to a published study showing a substance causes a specific disease. Epidemiological studies only point to a statistical correlation, the court said, while experts “bridge the gap between association and causation” with opinions based upon their training and experience.
The railroad argued the experts didn’t have scientific support for their claims Garner’s father was killed by exposure to diesel exhaust. Non-Hodgkin’s lymphoma is most closely associated with age and the medical consensus is 75% of cases have no known cause. The experts Garner hired said they could conclude that diesel exhaust had more than a 50% chance of causing his father’s disease, based on studies showing exhaust increases the overall risk of cancer by as much as 3875 cases per million.
It wasn’t necessary to point to specific research linking non-Hodgkin’s lymphoma to that overall risk figure, the appeals court said. While trial judges must be gatekeepers to prevent juries from being swayed by unscientific evidence, the court said, they also must be “cautious.”
“The trial court’s gatekeeping role does not involve choosing between competing expert opinions,” the appeals court said, citing a precedential ruling.
“Dr. Salmon gave a reasonable scientific explanation for his causation opinions, including his reliance on the overall cancer risk, and he cited objective, verifiable evidence supporting his opinions,” the court concluded. “BNSF submitted no evidence that his reasoning or methodology was scientifically invalid.”
In litigation over the heartburn medicine Zantac, Dr. Salmon was excluded from his opinion the drug, also known as ranitidine, could cause cancer. A federal judge ultimately dismissed thousands of Zantac lawsuits, citing a lack of expert scientific evidence.
Federal courts in Nebraska split on allowing Drs. Gale and Landolph to testify in lawsuits against Union Pacific over diesel exhaust, with one court rejecting them for lack of scientific basis for their opinions and the other letting them in.
“Dr. Gale must be able to say more than `Ronald was exposed to diesel exhaust; some unknown amount of diesel exhaust can cause cancer; therefore exposure to diesel exhaust caused Ronald’s lung cancer,’” said Magistrate Judge Cheryl R. Zwart in a 2020 order.
Bayer AG has offered to pay more than $10 billion to settle claims Roundup pesticide made by its Monsanto unit also causes non-Hodgkin’s lymphoma. Experts in that litigation opine even small exposures to the active ingredient glyphosate more likely than not cause the blood cancer, despite epidemiological studies involving tens of thousands of agricultural workers showing no link between glyphosate and non-Hodgkin’s lymphoma.