United States: First Circuit: Plaintiffs' Specific Causation Expert Fails to Pass Muster in Benzene Case

Last Updated: June 1 2016
Article by Rachel B. Weil

Last week, we (along with many of you, we assume) attended the DRI Drug and Medical Device conference in Chicago. We re-connected with friends dating to the beginning of our lengthy career (literally – ran into the head of our decades-ago summer associate program), met lots of new people, and attended great parties.  (Perhaps we are biased, but we thought the reception Reed Smith co-sponsored was particularly fabulous – stunning venue, fantastic food, great company and ambiance.)

Squeezed in among the parties was a whole seminar program, covering all manner of hot topics in the mass tort space in which we practice. We were (as we always are) awed by the sheer intellectual firepower the speakers brought to bear and by the depth of their knowledge and the thoroughness of their preparation.  We also enjoyed observing the diversity of presenters' styles.  Some were earnest and academic, some deceptively casual and colloquial, still others politician-impassioned.  As wordsmiths, we always delight in this, and we count it among the reasons we like today's case, which follows a mostly serious and measured (albeit dismissive) majority opinion with a snarky and stylized dissent.  (Guess which one was more fun to read.)

Milward v. Rust-Oleum Corp., 2016 U.S. App. LEXIS 7470 (1st Cir. Apr. 25, 2016), is not a drug or device case. It is the First Circuit's review of the District of Massachusetts's exclusion of the plaintiffs' specific causation expert in a benzene-exposure toxic tort case, but the issues are identical to Daubert issues we face in our cases.

The plaintiff-appellant worked as a pipefitter and refrigerator technician for over thirty years. In the course of his employment, he was exposed to varying levels of benzene from the defendant's products.  He was diagnosed with Acute Promylelocytic Leukemia ("APL"), and sued the defendant (among other parties gone from the suit by the time of this decision), alleging that its negligence caused his disease.

In earlier proceedings, the district court had excluded the plaintiffs' general causation expert, but that decision was reversed on appeal and remanded for consideration of the specific causation question. After discovery, the court granted the defendant's motion to exclude the plaintiffs' specific causation expert, and the appeal followed.

The majority explained that the expert had presented three theories. First, she testified that, "although benzene is naturally occurring, there is no safe level of benzene exposure." Milward, 2016 U.S. App. LEXIS 7470 at *4.   She "emphasized that she reached this conclusion by examining the biology, the pathophysiology, and what the substance does to the person and the disease process," id. (internal punctuation omitted), and "without relying on any of the relevant epidemiological studies." Id. Based on this "no safe level of exposure" theory, the expert concluded that the plaintiff's benzene exposure was the likely cause of his APL.   The district court "rejected this hypothesis because it could not be properly tested with any known rate of error." Id. Finding that the plaintiffs did not "meaningfully challenge" this holding on appeal, the court "assume[d] that the ruling was correct and bypassed[ed] further discussion of the issue." Id. (citation omitted).

Second, the expert "rather cursorily" concluded that "an individual's 'relative risk' of developing APL increases when exposed to specified amounts of benzene," according to certain epidemiological studies, that the plaintiff's exposure levels (calculated by another expert whom the district court did not exclude) was higher than the amounts those studies had found to be dangerous, and that benzene exposure likely caused the plaintiff's APL. Id. at *4-5.  "Notably," the court emphasized, the expert "did not explain why she chose the studies on which she relied, nor did she address any study with contrary findings." Id. at *5.  In her deposition, the expert confirmed that there were studies refuting her conclusion (finding, instead, that there is no relationship between benzene exposure and APL), but that she did not intend to weigh the different studies and offer an opinion about which should be considered and which should be discounted. Id.

Finally, the expert claimed that she engaged in a "differential diagnosis" (our colleague and co-blogger, Mr. McConnell, would emphasize that the correct term for this retrospective causation inquiry is "differential etiology") and ruled out common causal factors associated with APL, including smoking and obesity. She "then determined that since benzene exposure was a potential cause, she could also 'rule out' an idiopathic diagnosis (or a diagnosis without a known cause.)  Thus, since benzene exposure was the only significant potential cause remaining, she concluded that it was the likely culprit." Id.

The court made short work of both the expert's "relative risk" theory and her so-called "differential diagnosis." With respect to relative risk, the court rejected the plaintiffs' contention that, because no epidemiological studies directly contradicted the expert's "relative risk" opinion, the district court's holding – that the opinion lacked reliability because the expert failed to consider conflicting epidemiological studies – rested on an erroneous premise.  The court explained that it is not necessary that studies "present diametrically opposing conclusions to be in tension with one another," id. at *10, and that, while a number of studies show a correlation between APL and benzene exposure at a specific level, others do not show that correlation.  The expert chose a study that supported her conclusion, failed to account for those that didn't, and "the district court did not clearly err in finding that the studies were sufficiently distinct from one another such that utilizing one, rather than another, would necessarily lead to different testimony." Id. at *10-11.   The court also rejected that the plaintiffs' argument that the experts' statements about her unwillingness to consider divergent studies were taken out of context, holding that "there was no error in the district court's decision to give [the expert's] statements their plain meaning." Id. at *11.   Finally, the court rejected the plaintiffs' argument that, even if the district court did not err in any of the above respects, the expert's opinion was still admissible because it was based on reliable evidence.  The court noted that that, because the relevant studies "expressly cast each other into doubt," the district court "reasonably ruled that there needed to be some indication of why [the expert] utilized the studies that she did."   Id. at *14.  Absent such explanation, it was "impossible for the district court to ensure that her opinion was actually based on scientifically reliable evidence." Id.

With respect to the expert's so-called "differential diagnosis," the court explained that a valid differential diagnosis must show that the steps taking in ruling in and ruling out potential causes were "accomplished using scientifically valid methods." Id. at *16.  Here, the expert was "only able to 'rule out' an idiopathic APL because she had 'ruled in' benzene as a cause," id., a conclusion the court had already found unreliable.  The court held, "Under such circumstances, eliminating a number of potential causes – without properly and explicitly 'ruling in' a cause – is simply of little assistance." Id. (internal punctuation and citation to Restatement (Third) of Torts omitted).

As such, the court affirmed the district court's exclusion of the plaintiffs' specific causation expert and its consequent grant of summary judgment for the defendant. Suffice it to say that, by definition, the dissent disagreed, finding that the district court had abused its discretion on all of the issues.  But the dissent expressed this so delightfully that we almost forgot that it was wrong.  It used phrases like "call me unpersuaded," headings like "Setting the Stage" and "My Take on the Matter," and the verb "espy" (we love a clerk who uses the verb "espy").  We commend the majority opinion to your reference library and the dissent to your reading pleasure.  And, for all of you who missed DRI this year, we hope to see you there next year — hopefully somewhere, like Chicago, with rockin' pizza.

This article is presented for informational purposes only and is not intended to constitute legal advice.

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