Cooper v. Takeda Pharmaceuticals America, Inc.
239 Cal. App. 4th 555 (2015)
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Rule of Law:
An expert's opinion on medical causation is admissible if it is based on reliable methodology, such as a differential diagnosis, and need not definitively exclude every conceivable alternative cause of harm. A trial court's gatekeeping function is to exclude clearly invalid or unreliable opinions, not to resolve scientific controversies or require the expert to negate speculative alternative causes that lack substantial evidentiary support.
Facts:
- Takeda Pharmaceuticals manufactures Actos®, a prescription drug used to treat type 2 diabetes.
- In 2006, Jack Cooper was prescribed Actos® for his type 2 diabetes.
- Cooper took Actos® continuously for over five years, with a cumulative dose exceeding 50,000 milligrams.
- In November 2011, Jack Cooper was diagnosed with bladder cancer.
- Cooper had other potential risk factors for bladder cancer, including his age, race (White), gender (male), and a history as a light, former smoker.
- Medical records contained conflicting information about when Cooper quit smoking, with dates ranging from 1974 to the early 1990s.
- Cooper had worked as a construction supervisor for many years, but his medical records noted "no history of any occupational cause" of his cancer.
Procedural Posture:
- Jack and Nancy Cooper sued Takeda Pharmaceuticals in a California superior court (trial court).
- The case proceeded to a jury trial.
- The jury returned a verdict in favor of the Coopers, finding Takeda liable for strict liability and negligent failure to warn, and awarded them $6.5 million in damages.
- Takeda filed post-trial motions, including a motion for judgment notwithstanding the verdict (JNOV) and an alternative motion for a new trial.
- The trial court granted Takeda's motions, first striking the testimony of the Coopers' causation expert, Dr. Smith, as unreliable and speculative.
- Based on the exclusion of the expert testimony, the trial court granted the JNOV, finding insufficient evidence of causation to support the verdict, and also granted the motion for new trial.
- The trial court entered judgment in favor of Takeda.
- Nancy Cooper, as successor in interest for her late husband, appealed the trial court's post-verdict orders to the California Court of Appeal.
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Issue:
Did the trial court abuse its discretion by striking an expert's specific causation testimony as speculative and lacking foundation because the expert did not definitively rule out every other conceivable cause of the plaintiff's bladder cancer?
Opinions:
Majority - Aldrich, J.
Yes. The trial court abused its discretion by striking the expert's testimony and granting judgment notwithstanding the verdict. Under the substantial factor test for causation, a plaintiff's expert is not required to exclude every other possible cause of an injury with absolute certainty for their opinion to be admissible. The trial court misapplied its gatekeeping function by requiring Dr. Smith to rule out speculative causes for which there was no substantial evidence, such as unknown occupational exposures. Dr. Smith properly conducted a differential diagnosis by considering the most significant evidence-based risk factors, including Cooper's smoking history, and reasonably concluded based on numerous epidemiological studies that Actos® was the most substantial causative factor. The trial court overstepped its role by resolving scientific controversies over the validity of these studies, as flaws in individual studies go to the weight of the evidence for the jury to consider, not the admissibility of the expert's opinion.
Analysis:
This case significantly clarifies and limits the trial court's gatekeeping function regarding expert testimony in California, particularly in complex toxic tort and pharmaceutical liability litigation. It reinforces that under the standard set by Sargon, a court's role is to evaluate the reliability of an expert's methodology, not to weigh the evidence or choose between competing scientific conclusions. The decision provides crucial support for plaintiffs by affirming that an expert's causation opinion is admissible even when multiple risk factors are present, so long as the expert reasonably accounts for them. This precedent prevents defendants from defeating causation claims at the admissibility stage merely by pointing to speculative or unsubstantiated alternative causes.
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