New Jersey District Court Excludes Unreliable Plaintiff Expert Testimony Eliminating Need for First Valsartan Bellwether Trial

The first Valsartan-related (blood pressure medication) bellwether trial in the In Re Valsartan, Losartan and Irbesartan Products Liability Litigation, was set to begin last fall. However, New Jersey District Court Chief Judge Renee Marie Bumb (“the Court”) ruled that the opinions of the bellwether plaintiff’s causation expert regarding Valsartan’s role in causing the plaintiff’s liver cancer were largely unfounded and scientifically flawed. As a result of the Court’s finding, summary judgment was granted in favor of the manufacturers of the drug (“Defendants”) before the bellwether trial began. In Re Valsartan, Losartan, & Irbesartan Prods. Liab. Litig., Case No. 1:20-cv-00946 (D.N.J. Nov. 10, 2025) at 65-67.

The Valsartan litigation centers on claims that between January 1, 2012 and the summer of 2018, the medication was contaminated with carcinogenic nitrosamines – organic compounds produced by industrial processes. Id. at 3. More than 1,000 cases were filed following the recall of the drug in July 2018, and the cases were consolidated as Multidistrict Litigation (“MDL”) in the District of New Jersey. Id. at 4. The first bellwether trial in this MDL included allegations that the plaintiff began taking Valsartan in approximately September 2016, which caused him to develop hepatocellular carcinoma (“HCC”), a common and aggressive form of liver cancer. Id. at 4-5. The plaintiff was diagnosed with HCC in August 2018 and, unfortunately, passed away in March 2020. Id. at 5.

The plaintiff had an extensive history of liver problems, including abnormal liver function test results, hepatomegaly (enlarged liver), metabolic dysfunction-associated steatohepatitis (“MASH”), and cirrhosis, diagnosed in 2016. Id. at 5-10. In addition to the prior liver conditions, the plaintiff also suffered from other health ailments, including obesity dating back to 2008, and type 2 diabetes, diagnosed in 2016. Id. at 9.

Pre-Trial Motion Practice

Defendants filed a series of motions ahead of the anticipated trial date, including a motion to exclude the testimony of the plaintiff’s causation expert. Id. at 15. Defendants did not dispute the expert’s qualifications as a board-certified hematologist and medical oncologist with more than twenty clinical years of experience. Id. Rather, Defendants moved to exclude the testimony on the grounds that her opinions were flawed for failing to both reliably “rule in” the plaintiff’s exposure to the nitrosamines in Valsartan[1], and “rule out” the plaintiff’s numerous, well-established risk factors for the development of HCC. Id. The plaintiff and Defendants agreed that the Court’s resolution of the motion to exclude the expert testimony was case dispositive, and that without the testimony, the plaintiff lacked sufficient evidence to demonstrate specific causation. Id.

Legal Standard

Federal Rule of Evidence 702 governs the admissibility of expert testimony. The rule permits a qualified witness to testify in the form of an opinion, provided that the witness demonstrates to the court that it is more likely than not that a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or determine a fact in issue; b) the testimony is based on sufficient facts or data; c) the testimony is the product of reliable principles and methods; and d) the expert’s opinions reflect a reliable application of the principles and methods to the facts of the case. Id. at 11. As expressed in Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579 (1993), the court must act as a “gatekeeper” to prevent unreliable expert testimony from reaching the jury. Id. at 12.

Plaintiff’s Expert’s Opinions

The Court held a Daubert hearing to assess the plaintiff’s expert’s methodology and the reliability of her opinions. The expert testified at the hearing that, in her medical opinion, the plaintiff’s HCC was caused by his exposure to NDMA that was present in the Valsartan pills he consumed. Id. at 16. She further opined that the plaintiff’s other multiple risk factors for HCC, such as cirrhosis, MASH, diabetes, and obesity, were not substantial in causing the cancer. Id. The plaintiff’s expert performed a differential diagnosis to reach her conclusion, which involved ruling in and ruling out the possible causes and contributing factors of the plaintiff’s HCC. Id. 16. In her opinion, the plaintiff’s pre-existing risk factors should have caused a slow, step-like progression to developing HCC. Id. She opined that under normal circumstances (i.e., without exposure to NDMA), the plaintiff would not have developed HCC until approximately April 2023. Id. at 20. Plaintiff’s expert also relied on case studies that indicated a dose-response to developing cancer in rubber and dye factory workers who were exposed to NDMA occupationally, as well as three epidemiological studies that measured the association between NDMA in Valsartan and the risk of developing liver cancer. Id. at 21.

Findings and Conclusions

The Court held at the outset that there was no dispute that a differential diagnosis is a generally accepted method used to render specific causation opinions. Id. at 24. However, the Court agreed with Defendants’ position that the expert’s differential diagnosis was “speculative, result-oriented, and unscientific.” Id. at 25.

First, the Court criticized the expert’s opinion that the plaintiff only had “mild” liver cirrhosis as of April 2016, resulting in a “very minor increased risk” of developing cancer. Id. at 28. The evidence demonstrated that cirrhosis of the liver is the primary and most potent risk factor for the development of HCC. Id. at 27. Furthermore, relevant medical guidelines suggest that individuals with cirrhosis of any type immediately begin screening for HCC every six months. Id. The Court also examined the expert’s claim that the plaintiff’s timeline for developing HCC was inconsistent with the typical progression of cirrhosis because, in the expert’s opinion, the earliest date he would have developed HCC, but for his exposure to NMDA, was April 2023. Id. at 28. The Court found that this opinion was flawed because the expert improperly assumed that the plaintiff could not have developed cirrhosis before 2016 and based her opinion on an irrelevant study examining Hepatitis-C patients and HCC development, concluding that HCC typically develops seven to ten years after the development of cirrhosis.  Id. at 35-37.

Second, the Court took issue with the expert’s assumption that she could rule out all other risk factors (e.g., MASH, obesity, and diabetes) after she ruled out cirrhosis as a cause of the plaintiff’s HCC, because these risk factors were limited to the development of cirrhosis only, and not HCC. Id. at 39.  The Court found this opinion was significantly undermined by the great weight of scientific literature establishing that each of the plaintiff’s conditions was an independent risk factor for developing HCC, and concluded that the expert’s causation opinions were scientifically unreliable as she failed to perform a differential diagnosis for each of the plaintiff’s relevant risk factors. Id. at 40-50.

Finally, the Court criticized the expert’s reliance on studies where the authors explained that the results of the studies only represented a potential statistical association, not a definitive causal relationship, between NDMA exposure and cancer. Id. at 52. The plaintiff argued that NDMA is too toxic to test on humans ethically and that the expert should not be faulted for the lack of on-point studies. Id. at 51. The Court indicated that the lack of studies and research materials does not permit the expert to engage in wholesale speculation, and the expert cannot “rule in” NMDA exposure from Valsartan as a possible cause of the plaintiff’s HCC without reliable methodology. Id. The Court ruled, and excluded, the plaintiff’s causation expert’s opinion as unreliable, unsupported, speculative, and based on flawed methodology.

With the Court excluding the plaintiff’s expert’s opinion as unreliable, the Court granted summary judgment to Defendants because the plaintiff lacked sufficient evidence to demonstrate specific causation. The Court further dismissed the case in its entirety, with prejudice, relieving any remaining distributor defendants of liability as well.

Impact on Mass Tort Litigation

The Court’s ruling serves as a reminder of the scrutiny that trial courts are required to perform pursuant to Daubert as to litigants’ expert opinions, and the importance of utilizing reliable expert testimony and studies to support litigants’ claims and defenses. This decision will likely serve as a roadmap for plaintiffs to work through the flaws in their cases and rectify them through expert development and further medical research. Regarding this MDL, the liver cancer claimants make up only one of many classes of plaintiffs alleging that consumption of the medication caused their cancer. It is anticipated that additional bellwether trials with plaintiffs who developed other forms of cancer will go forward in this MDL at some point, and we expect similar expert challenges to occur in those cases.

[1] The specific nitrosamine alleged to have been consumed by Plaintiff is N-Nitrosodimethylamine (“NDMA”), which has been classified as a probable genotoxic carcinogen by the U.S. Food and Drug Administration (“FDA”). Id. at 3.