The judge overseeing the In re Roundup Products Liability Litigation MDL once remarked that “When you [consider] Ninth Circuit law, you come away with a pretty strong feeling that the Ninth Circuit is more tolerant of shaky expert opinions than other circuits.” But that was before the 2023 amendments to Federal Rule of Evidence 702, and appellate courts around the country have gradually been addressing how the amendments impact pre-amendment case law. The Ninth Circuit recently joined the ranks in a way, affirming that same judge’s exclusion of an expert’s causation opinion while harmonizing Ninth Circuit case law with the purposes of the 2023 amendments. The opinion is Engilis v. Monsanto Company, — F.4th —, 2025 WL 2315898 (9th Cir. 2025), and the headlines may come as a surprise to some.
The case-specific underpinnings of the holding are relatively straightforward. The plaintiff alleged that he developed cancer due to exposure to a product manufactured by the defendant. His expert, however, had failed to consider the plaintiff’s obesity as a potential cause of the cancer when conducting the differential etiology that formed his specific causation opinion. He tried to get around this omission by claiming that the plaintiff was not obese, and the plaintiff argued that this was a disputed fact because his plaintiff’s fact sheet was marked “negative” for obesity. However, the expert failed to cite any medical records indicating that the plaintiff was not obese and did not engage with records that showed he was obese. Translated to Rule 702 terms, any opinion that the plaintiff was not obese was not “based on sufficient facts or data.” So, the expert argued that obesity is not a risk factor for the kind of cancer at issue and thus did not need to be considered. But his report cited no support for that proposition, which he manufactured at the hearing on the defendant’s Rule 702 motion. The Ninth Circuit agreed with the district court that these issues rendered the expert’s specific causation opinion inadmissible.