Asbestos & Mass Tort Litigation

Key Points: 

• Supreme Court held that trial court misinterpreted the plaintiffs’ burden by stating Delaware Rule of Evidcen 702 should be applied with a liberal thrust favoring admission.
• Supreme Court ruled that the plaintiffs failed to show by preponderance of the evidence that their experts’ opinions were reliable.
• Court emphasized that “an expert offering an opinion regarding general causation for a product must opine as to the product itself,” not the toxicity of some individual component.
• Court observed that there is no consensus in Delaware law as to “threshold dose.”

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As of September 2022, there were approximately 75,000 pending Zantac (ranitidine) cases in Delaware, coming from more than a dozen national plaintiffs’ firms and with three Delaware firms acting as local counsel. These cases were filed in the Superior Court of Delaware.

The plaintiffs in In re: Zantac (Ranitidine) Litig., 2025 WL 1903760 (Del. 2025) alleged that their ingestion of the molecule ranitidine—marketed under the brand name Zantac, in which N-Nitrosodimethylamine (NDMA), an alleged carcinogen, may be found—caused the cancer with which they were diagnosed.

In November 2023, the defendants moved to exclude the plaintiffs’ general causation experts under Delaware Rule of Evidence 702 (DRE 702), which is modeled after Federal Rule of Evidence 702 (FRE 702), and the principles set forth in Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579 (1993), which determine whether expert testimony is admissible. Daubert reiterates the requirements of FRE 702 by stating that expert opinions must be the product of a reliable process measured by things like peer review and general acceptance in the scientific community. Daubert also states that judges should act as gatekeepers to ensure that potential expert opinions are both reliable and relevant before they can be heard by a jury. 

The defendants’ principal arguments were that (1) the original lab study was an outlier, conducted under unrealistic conditions, and the results were never duplicated; (2) the plaintiffs’ experts failed to offer threshold-dose opinions; and (3) the plaintiffs’ experts inappropriately focused on toxicity of NDMA itself as opposed to causation associated with ranitidine use.

The trial court denied the defendants’ Rule 702 motion, finding that (1) the studies focused on NDMA toxicity were sufficient to establish general causation—ignoring the defendants’ argument that no studies show a connection between ranitidine use and cancer; (2) Delaware law does not “recognize a threshold-dose requirement as part of the general causation analysis”; and (3) Delaware law requires a trial court to apply a “liberal thrust” favoring admissibility of expert testimony. Consistent with this liberal-thrust standard, the court dismissed each of the defendants’ critiques of the plaintiffs’ experts, stating that they went to weight rather than admissibility and, therefore, were jury questions. 

The defendants requested that the Superior Court certify its order for an interlocutory appeal. The Superior Court denied certification. However, the Supreme Court of The State of Delaware reviewed and granted the request. 

The Supreme Court acknowledged that evidentiary rulings are rarely appropriate for interlocutory review, but it noted that the trial court’s decision raised substantial issues regarding the Daubert standard and mass tort litigation specifically. Further, recognizing the significance of the issues, the Supreme Court elected to hear the case en banc.

The appellants raised three claims on appeal: 

(1)    The Superior Court applied an unduly lenient standard and wrongly held that all methodological critiques went to weight, not admissibility. Specifically, the appellants argued that an analysis under DRE 702 should not be conducted with a “liberal thrust favoring admission” and that it is a trial court’s duty to ensure that an expert applies his or her methodology reliably;
(2)    The Superior Court erred in focusing its general causation analysis on NDMA, rather than ranitidine; and 
(3)    The Superior Court erred in holding that the plaintiffs’ experts did not need to identify the threshold dose required to cause the cancers at issue.

On July 10, 2025, the Supreme Court reversed the trial court’s ruling on several grounds. 

First, the court held that the trial court misinterpreted the plaintiffs’ burden by stating DRE 702 should be applied with a liberal thrust favoring admission. The court stressed that Daubert never created a presumption of admissibility. Instead, they opined that “the proponent of an expert opinion must prove its admissibility by a preponderance of the evidence” with no presumption toward admissibility. 

After clarifying the burden of proof, the Supreme Court took a deep dive into the underlying studies. The court noted several instances where the plaintiffs’ experts ignored—without explanation—major peer-reviewed epidemiology studies in favor of lower-quality and less-relevant publications. In doing so, the court affirmatively ruled that the plaintiffs failed to show by preponderance of the evidence that their experts’ opinions were reliable. 

The Supreme Court also found that the trial court erred by framing the general-causation question on the alleged carcinogenic agent—NDMA—rather than the actual product at issue—ranitidine. The court emphasized that “an expert offering an opinion regarding general causation for a product must opine as to the product itself,” not the toxicity of some individual component. Having held that the plaintiffs’ experts’ opinions were deficient, the court determined that it did not need to reach the separate “threshold dose” question the defendants raised on appeal, but it observed that “there is no consensus in Delaware law as to ‘threshold dose.’”

There are several takeaways from the Supreme Court’s ruling that may be relevant to asbestos litigation. 

First, with the Delaware Supreme Court clarifying a preponderance-of-the evidence standard (with no presumption of admissibility) over the previously understood “liberal thrust favoring admission,” plaintiffs’ and defense experts are likely to face heightened scrutiny. 

Further, it now appears that experts offering causation opinions “must opine as to the product itself,” as opposed to asbestos toxicity generally. Plaintiffs may likely be required to show that exposure to a specific product has a higher rate of developing asbestos disease. This may pose a potentially significant obstacle for plaintiffs when asbestos fibers are encapsulated within a product. 

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_{Defense Digest, Vol. 31, No. 4, December 2025, is prepared by Marshall Dennehey to provide information on recent legal developments of interest to our readers. This publication is not intended to provide legal advice for a specific situation or to create an attorney-client relationship. ATTORNEY ADVERTISING pursuant to New York RPC 7.1. © 2025 Marshall Dennehey. All Rights Reserved. This article may not be reprinted without the express written permission of our firm. For reprints, contact tamontemuro@mdwcg.com.}