A while back we posted about an interesting toxic tort case involving important causation issues. See Zandi v. Wyeth, 2009 WL 2151141 (Minn.App.).  A Minnesota appeals court recently refused to rehear its prior affirmance of summary judgment for defendants in a suit by a woman who alleged hormone replacement drugs caused her breast cancer.  2009 Minn. LEXIS 648.

Plaintiff alleged that between approximately 1981 and 2001, she ingested hormone replacement therapy (HRT) drugs manufactured, designed, packaged, marketed, and distributed by defendants. In November 2001, Zandi alleges she was diagnosed with “hormone-dependent breast cancer.” She contended that the HRT drugs caused her cancer.

The trial court found that plaintiff’s specific causation evidence did not satisfy Minnesota’s standard for admissibility of expert testimony. Zandi offered testimony from Dr. Lester Layfield and Dr. Gail Bender to try to prove that HRT drugs caused her cancer. Minnesota courts use the Frye standard to determine the admissibility of novel scientific evidence. Zandi’s claims were based on the following propositions: 1) it is supposedly generally accepted that HRT causes hormone-dependent breast cancer, and 2) there is a generally accepted method of diagnosing the cause of hormone-dependent breast cancer in an individual. The appellate issues revolved around the second.

Plaintiff’s experts based their specific causation opinions in part on “differential diagnosis.”  As readers of MassTortDefense know,  differential diagnosis, sometimes called “differential etiology”  is a process through which all the scientifically plausible causes of an injury are “ruled in,” and the expert then “rules out” the less plausible causes until reaching the one that theoretically cannot be ruled out.  If you’ve watched “House” on TV, you have seen the use of differential diagnosis to discover what disease a patient is suffering from.  Less traditional, and more questionable, is the use of the technique to discover what is the cause of the disease in the patient.  Most doctors don’t care as much about the cause of the disease as getting the right disease and treating it.  As used by toxic tort plaintiffs, differential diagnosis adopts a process of elimination to identify not just the injury (which may be debated) but also the cause; in theory, it seeks to eliminate the possibility of competing causes or confounding factors.

Again, in performing a differential diagnosis, a physician begins by ruling in all scientifically plausible causes of the patient’s injury. The physician then rules out the least plausible causes of injury until the most likely cause remains. Yet, breast cancer does not lend itself to such a differential diagnosis because the scientific community has not accepted that breast cancer has a limited number of discrete and recognized possible causes such that ruling out one or a few causes would necessarily implicate another. For differential diagnosis to be sufficiently reliable to even come close to proving causation, even assuming one accepts the method in this context, the diagnostician should rule out all other hypotheses, or at least explain why the other conceivable causes are excludable. But additional risk factors that plaintiff failed to adequately account for here in this case included family history. When faced with this dilemma, as is common when a disease has many idiopathic cases, plaintiff’s experts simply suggest that it is possible to conduct a reliable differential diagnosis without ruling out other hypotheses, as long as “major” or “most” explanations are ruled out.  Courts should be wary of this.

Courts generally recognize that the proffered expert must have a sufficient basis to “rule in” the drug or toxic substance at issue as a plausible cause of plaintiff’s injury. E.g., Jazairi v. Royal Oaks Apts., 217 Fed. Appx. 895 (8th Cir. 2007).  But this case is a good reminder that the plaintiff’s expert testimony must also reliably “rule out” the other plausible causes of the injury–  again, especially difficult when its causes are largely unknown.  On this record, the court said, “We conclude that there is not a method of diagnosing the specific cause of a particular woman’s breast cancer that is generally accepted in the relevant scientific community. This reality leaves Zandi without a legally sufficient ability to prove specific causation.”  See also Perry v. Novartis, 564 F. Supp.2d 452 (E.D. Pa. 2008).

This clear reasoning can be contrasted with the inexplicable finding of the 8th Circuit in Scroggin v. Wyeth, 2009 WL 3518245 (8th Cir. Nov. 2, 2009), which accepted plaintiff’s carefully constructed circular reasoning.  Unable to prove that the breast cancer was caused by hormone therapy drugs, plaintiff’s expert simply re-diagnosed the disease as hormone-induced breast cancer.  This allowed the expert to engage in a so-called differential diagnosis to determine the cause of the breast cancer simply by ruling out the two possible sources of these hormones: (1) plaintiff produced the hormones herself, or (2) they came from the hormone replacement therapy she had allegedly taken for the past eleven years.  Under this circular reasoning, any form of cancer can easily be linked to the defendant’s product because it will be re-characterized as the sub-type of disease caused by the substance at issue.