Expert’s Drug Causation Testimony Admissible Despite Acknowledgment Of Other Independent Causation Risks

In litigation for failure to warn of breast cancer risk from hormone replacement therapy, admitting plaintiff's expert’s testimony about specific causation (that the defendant's hormone replacement drugs were the cause of the plaintiff's breast cancer); the fact that the plaintiff also had independent "breast cancer risk factors and a family history" of breast cancer did not undermine the admissibility of the expert's differential diagnosis that the plaintiff's cancer "would not have developed without hormone replacement therapy," in In re Prempro Products Liability Litigation, 586 F.3d 547 (8th Cir. Nov. 2, 2009) (Nos. 08-2555, 08-2711, 08-2713)

A 2002 report in the Journal of the American Medical Association noted findings by a decade-long study of the Women's Health Initiative. The report was alarming because it concluded that women undergoing menopausal hormone replacement therapy were "twenty-four percent more likely to develop breast cancer than the control group," who received a placebo. Hormone replacement drugs, which had once been a major profit center for certain drug companies turned into a source of new product liability suits. One liability theory centered on the contention that makers of the hormone replacement drugs failed to warn of the danger of breast cancer. A recent Eighth Circuit case explores the admission of expert evidence regarding proof of specific causation of a victim’s breast cancer: Did the hormone replacement drug that caused a victim’s cancer if that victim also had other risk factors, such as family history, for breast cancer in the absence of hormone replacement?

In the case, plaintiff Scroggin was diagnosed with breast cancer eleven years after starting hormone replacement (estrogen and progestin) therapy with drugs made by defendants Wyeth Pharmaceuticals and Upjohn. After the plaintiff incurred a double mastectomy and chemotherapy treatment, she sued the defendants for failure to warn of the breast cancer risk from the hormone replacement therapy. According to the circuit: “the FDA still considers the drugs [taken by plaintiff] safe and effective. The FDA now requires, however, the drugs' labels to reflect the results of the WHI study, and … contain a boxed warning of the risk of breast cancer. Following the release of the WHI results, the number of prescriptions dropped significantly. This drop in prescriptions was accompanied by a corresponding reduction in the number of cases of breast cancer diagnosed in the United States. Likewise, a retrospective review has since shown that breast cancer increased as prescriptions for hormone replacement therapy increased.” Prempro Products Liability Litigation, 586 F.3d at 562.

The plaintiff’s contention at trial was that the defendants misleadingly minimized the known risks of their drug. The jury decided for the plaintiff. The defendants appealed, contending in part, that the trial court erred by admitting testimony from the plaintiff’s expert (Scroggin), a doctor, as to the specific cause of her cancer. The defendants claimed that the plaintiff’s evidence “failed to prove that their drugs were the cause of her injury.” Rather than their drug, they contended that the plaintiff’s “family history of breast cancer” including her “various risk factors for breast cancer, such as breast density, her age, weight, and her smoking history” accounted for the cancer. The defendants did not challenge the qualifications of the plaintiff’s causation expert and they did not “argue that the method she used, differential diagnosis, is not a sound and accepted methodology. Instead, they argue[d] that differential diagnosis cannot be used to prove the cause of breast cancer because no one knows the cause of breast cancer.” Prempro Products Liability Litigation, 586 F.3d at 566. In essence, they did not challenge the reliability of the methodology of differential diagnosis. Rather they challenged that the methodology was properly applied in the plaintiff’s case.

The Eighth Circuit found no error in admitting the expert’s opinion testimony based on a differential diagnosis analysis. A differential diagnosis is a technique in which the expert engages in a “patient-specific process of ruling out potential causes of an illness as unlikely, until one cause remains” as the likely cause of a condition. See Ruggiero v. Warner-Lambert Co., 424 F.3d 249, 251-52 (2d Cir. 2005) (“A differential diagnosis is ‘a patient-specific process of elimination that medical practitioners use to identify the “most likely” cause of a set of signs and symptoms from a list of possible causes.”) (citing Hall v. Baxter Healthcare Corp., 947 F.Supp. 1387, 1413 (D.Or. 1996)))

The circuit noted that at trial the plaintiff’s oncologist, “tested the tumors in Scroggin's breasts for hormone receptors to inform her treatment. Both the left and right tumors were one hundred percent positive for estrogen and progesterone receptors. There was no dispute at trial that hormone-receptor-positive tumors are dependent upon hormones for their growth. Moreover, published research had concluded that hormone-receptor-positive tumors need hormones to grow, that menopausal symptoms result from hormone deficiency, and that there is a link between breast cancer and hormone replacement therapy.” Prempro Products Liability Litigation, 586 F.3d at 566.

The causation expert could rely on the other expert’s testimony that the plaintiff’s “breast cancer was hormone dependent.” With this information, the plaintiff’s expert “sought to determine the cause of Scroggin's breast cancer by ruling out the two possible sources of these hormones: (1) Scroggin produced the hormones herself, or (2) they came from the hormone replacement therapy she had taken for the past eleven years. Scroggin presented evidence that her menopausal symptoms were relieved by hormone replacement therapy, confirming that her own body was unable to produce sufficient hormones and therefore could not be the cause. The remaining source was the combination of [defendants’ drugs] Premarin, Provera, and Prempro. Accordingly, Scroggin presented evidence establishing a causal link between breast cancer and estrogen plus progestin use, particularly for the length of time Scroggin was taking the drugs.” Prempro Products Liability Litigation, 586 F.3d at 566 (footnote omitted).

The circuit specifically rejected that the expert’s acknowledgment that the plaintiff has other risk factors for breast cancer undermined the reliability of his differential diagnosis:

“We find unpersuasive the contention that Dr. Naftalis's testimony should not have been admitted because Scroggin has some breast cancer risk factors and a family history of breast cancer. Dr. Naftalis sufficiently established that hormones were necessary to the development of Scroggin's tumors and conducted her differential diagnosis from this starting point. Although not necessary to the formation of her opinion, Dr. Naftalis addressed the known causes of breast cancer and possible risk factors. Wyeth and Upjohn argue that this review was insufficient, but Dr. Naftalis's “explanations as to conclusions not ruled out went to weight and not admissibility .” Additionally, Scroggin submitted to every available genetic test for breast cancer, all of which came back negative for the most common breast cancer genes. Wyeth's genetics expert testified that he continues to believe that genetics caused Scroggin's breast cancer, but the jury concluded otherwise.”
Prempro Products Liability Litigation, 586 F.3d at 566 (citation omitted).


The circuit noted that while the expert’s opinion was not beyond challenge, that was not the test for admissibility of expert opinion. It found that the expert’s ability “to testify that Scroggin's breast cancer would not have developed without hormone replacement therapy because Scroggin's body was not producing sufficient amounts of hormones to allow hormone-receptor-positive tumors to develop. Thus, Dr. Naftalis ruled out the other possible cause of Scroggin's breast cancer, and her expert testimony was properly admitted. Wyeth and Upjohn had the opportunity to expose the testimony's weaknesses through vigorous cross-examination and the presentation of contrary evidence.”

For other posts discussing the use of differential diagnosis, see:

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