## Facts

- Jack Cooper, who had type 2 diabetes, was prescribed Actos (pioglitazone) in 2006 and took it continuously until a bladder-cancer diagnosis in November 2011, consuming over 50,000 mg over about five years.
- Jack and Nancy Cooper sued Actos’s manufacturer entities for strict liability failure to warn, negligent failure to warn, and loss of consortium (Nancy).
- Plaintiffs’ causation expert, a urologic oncologist, opined that Actos was the most substantial causative factor in Jack’s bladder cancer and a substantial factor in bringing it about.
- The expert relied on medical records, clinical experience, and multiple epidemiological studies and used differential diagnosis, including consideration of alternative risk factors such as Jack’s remote smoking history.
- The jury returned a verdict for plaintiffs and awarded $5 million to Jack and $1.5 million to Nancy.
- Post-verdict, the trial court struck the expert’s causation testimony as speculative and unreliable, granted judgment notwithstanding the verdict (JNOV) for defendants, and alternatively granted a new trial.
- Nancy Cooper (individually and as successor in interest) appealed.

## Issues

1. Whether the trial court erred by striking plaintiffs’ expert causation testimony as speculative or lacking foundation.
2. Whether, with the expert testimony admitted, substantial evidence supported the jury’s finding that Actos was a substantial factor in causing bladder cancer.
3. Whether the trial court improperly required the expert to rule out all other possible causes (including smoking) to satisfy California’s substantial-factor causation standard.
4. Whether the evidence supported instructing the jury on concurrent or multiple causation.

## Decision

- The Court of Appeal reversed the JNOV and the order granting a new trial and directed entry of judgment on the jury’s verdict for plaintiffs.
- The trial court abused its discretion in striking the expert’s causation testimony by applying an unduly stringent admissibility standard.
- The expert’s differential-diagnosis methodology, supported by epidemiological evidence (including studies showing increased risk with long-term/high-dose use), was admissible and constituted substantial evidence of specific causation.
- The evidence warranted a concurrent/multiple-causation instruction because Actos and other factors could each be substantial factors.
- Because admissible evidence supported the verdict, neither JNOV nor a new trial was proper.

## Legal Principles

- In assessing admissibility of expert causation opinions, a court may evaluate methodological reliability and factual foundation but may not require an expert to disprove every alternative hypothesis.
- Under California’s substantial-factor test, a product need not be the sole cause; liability may attach if the product was a substantial factor contributing to the injury.
- Differential diagnosis may support specific causation when the expert reasonably considers plausible alternative causes and explains why the defendant’s product remains a substantial factor.
- Epidemiological evidence, combined with a patient-specific clinical assessment, may support a finding that exposure more likely than not contributed to the plaintiff’s injury.
- A multiple/concurrent-causation instruction is appropriate where evidence shows more than one potential substantial factor may have contributed to the harm.

## Conclusion

The Court of Appeal reinstated the plaintiffs’ jury verdict, holding that the trial court improperly excluded causation testimony by demanding a rule-out-all-causes showing, and reaffirming that differential diagnosis and epidemiological evidence can provide substantial evidence of specific causation under California’s substantial-factor standard, including in cases involving potential concurrent causes.


Cooper v. Takeda Pharms. Am., Inc., 239 Cal. App. 4th 555 (Cal. Ct. App. 2015)