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On July 12, 2014, in Bostic v. Georgia Pacific Corp., No. 10-0775, a six-justice majority of the Texas Supreme Court issued a major decision on causation in asbestos cases. The Court held that the requirement to provide evidence of approximate dose announced in Borg Warner v. Flores, 232 S.W.3d 765 (2007), applies to mesothelioma cases, not just asbestosis cases. The Court expressly rejected the Court of Appeals statement that the plaintiffs had the burden of proving that exposure to the defendant’s product was a “but for” cause of his mesothelioma. The Court elaborated on Flores by holding that a plaintiff who alleges exposures to asbestos from multiple sources must prove that the exposures attributed to each defendant are substantial compared with exposures from other sources. The Court concluded that the plaintiffs’ evidence of causation was legally insufficient.

Legal Background
There are two Texas Supreme Court decisions that can be described as foundational on the question of causation in toxic tort cases. The first is Merrell Dow Pharmaceuticals, Inc. v. Havner, 953 S.W.2d 706, 714-15 (Tex. 1997), where the court held that causation must be proved by either direct evidence of causation or through two or more epidemiological studies showing that exposures similar to those alleged by the plaintiff cause a statistically significant doubling of the risk. In the second, the Flores decision, the Supreme Court held that the plaintiff must present evidence (1) of the approximate dose of asbestos attributable to the defendant, (2) that the dose was sufficient to cause the plaintiff’s disease and (3) that the dose was a substantial factor in causing the disease. The injury at issue in Flores was asbestosis. In an effort to avoid application of the Flores decision, the plaintiffs have argued that Flores does not apply to mesothelioma cases because mesothelioma may result from significantly lower levels of exposure than are required for asbestosis. The Texas Supreme Court addressed this argument in the Bostic case.

The Bostic Case
Bostic died from mesothelioma that the plaintiffs alleged was caused by his exposure to asbestos-containing Georgia Pacific joint compound. Bostic testified that from childhood through his teenage years he was exposed to chrysotile-containing Georgia Pacific joint compound that his father used on construction jobs. The plaintiffs initially sued 39 defendants, but Georgia Pacific was the only remaining defendant at the time of trial.

To prove causation, the plaintiffs relied on testimony from three experts, Arnold Brody, Richard Lemen and Samuel Hammar, who testified that mesothelioma is a dose-related disease, but they did not attempt to quantify Bostic’s exposure from Georgia Pacific joint compound. Instead, they testified that there is no identified threshold of exposure below which mesothelioma will not occur and, consequently, that all exposures above background cause mesothelioma.

The Fort Worth Court of Appeals reversed and rendered judgment for Georgia Pacific. The court determined that the plaintiffs had failed to meet their burden of proving that the Georgia Pacific joint compound was a “but for” cause of Bostic’s mesothelioma. The plaintiffs petitioned the Supreme Court for review. They argued that “but for” causation is the incorrect standard, and that Flores’s dose requirement is inapplicable when the plaintiff has mesothelioma.

The Majority
The Texas Supreme Court majority held that Flores’s requirements apply to mesothelioma cases, and that the plaintiffs’ “any exposure above background” testimony was not evidence of causation. The majority rejected the Court of Appeals’s statement that proof of “but for” causation is required in asbestos cases. The Court adopted a new requirement for proof of substantial causation in cases involving exposure to a toxin from multiple sources.

Every exposure: The Court critiqued the theory that every exposure above background causes mesothelioma. This theory, the Court explained, is inconsistent with the principle, admitted by the plaintiffs’ experts, that mesothelioma is a dose-response disease. The Court warned that the theory relieves plaintiffs of their burden to prove causation, and would lead to imposition of “absolute liability against any company whose asbestos containing products” cross the plaintiff’s path. The Court faulted the logic of every exposure because it posits that all exposures above background cause disease while ignoring the possible causal role played by background exposures.

"But for" causation: The Court reaffirmed that Flores does require proof of "but for" causation. The Court engaged in a lengthy discussion of the Restatement Third of Torts and concluded that the plaintiffs were required to prove that the Georgia Pacific joint compound was a substantial factor in bringing about Bostic’s mesothelioma, not that it was a "but for" cause of his mesothelioma.

Proof of substantial factor: The Court elaborated on, and arguably expanded, Flores. Drawing on Havner, the Court held that in the absence of direct evidence, the plaintiff must link the defendant’s product to his injury through expert testimony based on reliable epidemiological studies showing that similar exposures double the risk of the plaintiff’s disease.

The Court required the plaintiff to show that the exposure attributed to the defendant is substantial when compared with exposures from other sources. In Flores, the Supreme Court suggested that such comparative evidence is required, but this requirement was not adopted by Texas appellate courts and was rejected by the statewide asbestos MDL court. The Court suggested that this comparative proof should take the form of epidemiological studies. By way of illustration, the Court stated that exposure from one source that merely doubles the plaintiff’s risk is not a substantial factor when it is compared with an exposure from another source that carries a 10,000-fold increase in risk.

After setting out these principles, the Court evaluated the evidence and held that there was no evidence that exposures to Georgia Pacific drywall compound caused Bostic’s mesothelioma. The plaintiffs did not attempt to quantify the exposure attributable to Georgia Pacific, and the experts cited no literature that established a statistically significant link between Bostic’s occasional exposure to joint compound and his mesothelioma.

The Dissent
The Dissenters, Justices Lehrmann, Boyd and Devine, would have concluded that there was sufficient evidence of causation. The dissent criticized the majority’s use of Havner, arguing that Havner applies only to proof of general causation or whether a substance is capable of causing a disease, and not specific causation or whether the exposures in question caused the plaintiff’s disease. Additionally, the dissent would not require the plaintiff to prove that exposures attributable to the defendant are alone sufficient to cause his disease. The dissenters, instead, would allow proof that the exposures attributed to the defendant contributed to a total dose that is sufficient to cause the disease. The dissent asserted that “every exposure” mischaracterized the theory offered by the experts. Rather, the experts only opined that every exposure increases the risk of disease by contributing to total fiber burden.

The Concurrence
Justice Guzman concurred in the result, but disagreed with the majority’s approach. She faulted as too exacting the majority’s requirement that epidemiology show that the exposures attributed to the defendant doubled the plaintiff’s risk. She further argued that requiring comparative proof of exposures is contrary to the comparative fault statute.

Discussion
Bostic answers significant questions left open by the Texas Supreme Court in Flores. First, the Court now holds that Flores is applicable to mesothelioma cases, and not just asbestosis claims. While Texas appellate courts and the statewide asbestos MDL court had applied Flores to mesothelioma cases, the Texas Supreme Court has now spoken on this point.

Second, the Court held that proof of substantial-factor causation must take into account the comparative role played by exposures from different sources. In Flores, the court eluded to this requirement, but the requirement had not been adopted by lower courts.

A third significant point is the Supreme Court’s adoption of Havner in cases where there are multiple sources of exposure to a single substance. In doing so, the Court made explicit that the requirements of Havner are applicable to both specific and general causation.