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See the 60-second demo →In August 2025, the Ninth Circuit affirmed summary judgment for Monsanto in Engilis v. Monsanto Co. The plaintiff's oncology expert — board-certified, qualified, well-prepared on the toxicology — was excluded for one reason. He had performed a differential etiology to link the plaintiff's chronic lymphocytic leukemia to glyphosate exposure, and along the way he had not ruled out obesity. He had not examined the plaintiff. He had not reviewed weight or BMI records. When asked at deposition whether the plaintiff was obese, he conceded he could not say.
That was the case.
If you are a plaintiff attorney with a toxic-tort or product-liability case riding on differential etiology, Engilis is the cleanest cautionary tale to come out of the post-amendment FRE 702 era. And the fix is short.
The plaintiff alleged that long-term glyphosate exposure caused his CLL. His oncology expert performed a differential etiology — the standard methodology for a single-plaintiff specific-causation opinion. Differential etiology, applied properly, means: identify the universe of recognized causes of the plaintiff's disease, then walk through each one and rule it in or rule it out based on the patient's actual record.
For CLL, the recognized causes include — at minimum — age, family history, prior infections, certain occupational chemical exposures, and, increasingly in the literature, obesity. The expert identified the universe correctly. What he did not do was apply it to this plaintiff.
The Ninth Circuit framed the failure as a missing factual basis rather than a methodology gap. The expert had never seen the plaintiff in person. He had not pulled BMI from the chart. He had not asked his retaining attorney to send him weight history. When obesity came up at deposition as a known CLL risk factor, the expert could only say he did not know. The Ninth Circuit affirmed the district court's summary judgment for Monsanto. The case ended.
Engilis sits inside a recurring pattern. Every recent toxic-tort general-causation MDL — Acetaminophen, Paraquat, Zantac in its federal incarnation — has produced a defining plaintiff-expert exclusion on a related theme: the alternative cause was not addressed.
In Engilis the alternative was obesity. In the Maryland Bayview/Hopkins birth-injury decision in 2025, it was prematurity. In the 2024 Maryland brachial-plexus case, it was maternal forces. In the 2018-but-still-controlling Mirena IIH MDL, it was the recognized non-Mirena causes of idiopathic intracranial hypertension. The defense bar has internalized the lesson. The next motion they file will tell your expert exactly which alternative cause was not ruled out, and the court will agree.
What makes Engilis especially marketable to the defense bar — and especially dangerous to plaintiffs — is that the expert was concededly qualified. He had the right specialty. He had the right credentials. He had a defensible methodology. What he did not have was a written rule-out of obesity rooted in the plaintiff's own chart. That is the kind of gap that used to be cross-examination material. After the December 2023 amendment to FRE 702, it is admissibility material.
The amendment formalized what the Fourth Circuit had already said in Sardis v. Overhead Door: reliability is admissibility, not weight. An expert who cannot ground a key part of his methodology in case-specific facts has not "reliably applied" the methodology — and the proponent has not carried the preponderance-of-the-evidence burden of admissibility. Courts that used to send these arguments to the jury are now resolving them at the gate.
For your case, the implication is direct. If your differential-etiology expert has not pulled the alternative-cause data from the chart and addressed each one in writing, you have an Engilis exposure. The defense motion will write itself.
Three concrete steps:
1. Build a written alternative-cause checklist for the diagnosis at the start of the engagement. For every common cancer claim there is a recognized list of risk factors in the literature. CLL: age, family history, prior infections, occupational exposures, obesity. NHL: similar but with HCV and immunosuppression added. Breast cancer: age, family history, BRCA status, hormone replacement, alcohol, BMI. Pull the list before the expert writes a word. Make it the spine of the report's specific-causation section.
2. Require physical-record citation for each rule-out. It is not enough for the expert to say "obesity considered." The report should cite the specific records — chart notes, vital signs, BMI calculations — that the expert reviewed in ruling obesity in or out. If the records do not exist or were not produced, that is itself a finding to flag for case strategy. Better to surface the gap during expert engagement than to discover it during deposition.
3. Run a deposition-prep audit on the alternative-cause checklist. Before the expert is deposed, walk through every alternative cause with the expert and confirm that the rule-out is anchored in the plaintiff's record. Any answer that begins "I don't recall whether the chart…" or "I'd have to check…" is a Daubert motion exhibit. The Engilis expert's "I cannot say whether the plaintiff was obese" answer was the entire case.
Two broader points:
The first is that case-specific differential etiology is one of two related methodologies that the post-2023 amendment has destabilized. The other is meta-analytic general causation — the methodology at issue in the Paraquat MDL and in the Wells exclusion. If your case requires both general and specific causation, both methodologies need to be hardened. The Paraquat lesson is that meta-analytic study-selection criteria have to be written down before the studies are selected; the Engilis lesson is that the rule-outs have to be physically grounded in the plaintiff's chart. Different methodologies, parallel weaknesses.
The second is that experienced experts are not protected by their experience. Schneider in Engilis was board-certified in oncology. Adler in Scottoline was a pediatric neurologist. Their credentials did not save them. What would have saved them is a workup that anticipated the defense motion. That is now the fundamental Daubert posture: the report has to look like the gatekeeping order before the gatekeeper writes one.
MedLegal AI's Daubert workup tool runs every retained expert's draft report through an alternative-cause matrix tied to the specific diagnosis. For oncology, the tool auto-pulls the documented alternative causes from the medical literature — including BMI — and flags any cause that has not been addressed with a record citation. For birth injury, it pulls prematurity, infection, pre-eclampsia, and genetic/metabolic screen results. The tool surfaces exactly the gaps the Engilis expert had: alternative cause identified, no rule-out documented, no record citation. The point is to prepare smarter for Daubert challenges — to give your expert a written rule-out for every alternative the defense will press at deposition. You can run a free Daubert workup on your expert here.
Engilis is the cleanest 2025 cautionary tale for plaintiff differential-etiology cases. A qualified expert, a defensible methodology, and a single missing rule-out — and the case ended. The fix is small, specific, and inexpensive. Build the alternative-cause checklist at the start, anchor each rule-out to the chart, and audit the deposition prep before it happens. The cases surviving Daubert in 2026 will be the ones whose specific-causation reports are unrecognizable from the Engilis expert's.
Run a free Daubert workup on your expert.
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