Dupixent Side Effects Lawsuit Alleges Drug Caused Cutaneous T-Cell Lymphoma

Lawsuit claims five months of Dupixent use led to a CTCL cancer diagnosis and the need for life-long treatment.

A product liability lawsuit alleges the makers of Dupixent knew the eczema treatment could increase the risk of a rare form of cancer, but failed to adequately warn patients or the medical community.

The complaint (PDF) was filed by Anna Tsang in the U.S. District Court for the District of Connecticut on September 16, naming Dupixent’s manufacturers, Regeneron Pharmaceuticals Inc., Sanofi-Aventis U.S. LLC and Genzyme Corporation, as defendants.

Tsang says she used Dupixent for only a few months before being diagnosed with a rare form of T-cell lymphoma. The lawsuit alleges the manufacturers failed to adequately investigate the cancer risk and continued marketing the drug despite evidence that should have prompted further testing and safety action.

Dupixent Cancer Risks

Dupixent (dupilumab) was first approved in 2017 by the U.S. Food and Drug Administration (FDA), originally for the treatment of atopic dermatitis, which is a form of eczema. However, the manufacturers repeatedly, and successfully, petitioned the agency to grant numerous additional approvals for the use of Dupixent.

It is now used for the treatment of a variety of different skin and respiratory conditions, including asthma, chronic obstructive pulmonary disease (COPD) and other health problems caused by overactive immune systems.

However, in recent months, the FDA and manufacturers have seen a rise in reports of adverse Dupixent side effects after patients indicate they have been diagnosed with cutaneous T-cell lymphoma (CTCL), a form of T-cell lymphoma that primarily affects the skin. In addition to causing CTCL, some patients report that it may also cause flare ups in those already battling the cancer.

The manufacturers now face a growing number of Dupixent lawsuits, each alleging the drugmakers failed to warn doctors properly of the risks of cancer and the need for close patient monitoring.

Dupixent T-Cell Lymphoma Allegations

According to Tsang’s lawsuit, she was originally prescribed Dupixent in May 2025 for the treatment of eosinophilic esophagitis, an autoimmune disorder that causes white blood cells to build up in the lining of the esophagus. It can cause swelling, tissue damage and difficulty swallowing.

Tsang took Dupixent injections until October 2025, when she was diagnosed with CTCL. She has since gone through phototherapy and radiation therapy and will likely require medical treatment for her cancer indefinitely, the lawsuit claims.

“Defendants failed to timely and adequately warn Plaintiff and her medical providers of the propensity of Dupixent to cause the development or accelerate the progression of CTCL, and the need to get appropriate diagnostic tests before initiating Dupixent treatment and during such treatment, despite Defendants’ knowledge of same. Defendants also failed to warn Plaintiff and her medical providers to cease use of Dupixent upon suspicion of CTCL.”

– Anna Tsang v. Regeneron Pharmaceuticals Inc. et al.

The lawsuit indicates that if Tsang’s doctors had been properly warned about the risks they would have passed on that information to the plaintiff, performed additional testing, and either never prescribed Dupixent or taken her off the drug when the first signs of CTCL appeared.

Tsang alleges that the scientific data about Dupixent cancer risks was available before she was first prescribed the medication, but the companies decided to keep that information from consumers and the medical community to preserve profits from the drug’s numerous approved uses.

The lawsuit claims the defendants’ actions prevented the plaintiff and her physicians from reasonably discovering that she faced a risk of developing CTCL or that the defendants’ conduct allegedly caused those risks.

Tsang presents claims of failure to warn, negligence, negligent misrepresentation and breach of warranty. She seeks both compensatory and punitive damages.

Dupixent Cancer Lawsuits

The claim will be consolidated with similar Dupixent cancer lawsuits in the District of New Jersey as part of a multidistrict litigation (MDL) before U.S. District Judge Zahid N. Qurashi, who is overseeing coordinated discovery and pretrial proceedings.

Judge Qurashi is expected to direct attorneys to prepare several cases representative of most of the litigation to serve as “bellwether” trials. These early test cases are designed to provide an opportunity to see how juries respond to the strengths and weaknesses of arguments and evidence.

While the outcomes of these trials are not binding on other claims, the results may help attorneys negotiate a Dupixent cancer lawsuit settlement or other resolution to the lawsuits. However, if the litigation is not resolved after pretrial proceedings and selected cases are completed, the remaining claims are likely to be remanded to their originating federal court districts for individual trials.

Sign up for more legal news that could affect you or your family.