Dupixent Cancer Lawsuit Filed Over Cutaneous T-Cell Lymphoma (CTCL) Diagnosis

Woman says she was diagnosed with stage IV cancer due to Dupixent manufacturers failing to adequately warn of T-cell lymphoma risks.

An Illinois woman indicates in a recently filed product liability lawsuit that she was diagnosed with mycosis fungoides and Sézary syndrome, both of which are forms of T-cell lymphoma that developed as a direct result of being injected with the biologic medication Dupixent, which is widely used to treat several chronic inflammatory conditions.

The complaint (PDF) was brought by Alison Walsh in the U.S. District Court for the Northern District of Illinois on December 16, naming Regeneron Pharmaceuticals Inc. and Sanofi-Aventis LLC as the defendants.

Dupixent (dupilumab) was approved by the U.S. Food and Drug Administration (FDA) in 2017, as an injection administered every two to four weeks for treatment for atopic dermatitis, also known as atopic eczema. It has subsequently been approved to treat asthma, chronic obstructive pulmonary disease (COPD) and other inflammatory diseases affecting the respiratory tract and skin, with more than 1 million patients receiving the injection in recent years.

Although the drug has been marketed as safe and effective, as soon as the treatment hit the market concerns began to emerge about a potential link between Dupixent and T-cell lymphoma, a rare cancer affecting white blood cells. Reports have associated the drug with increased risks of cutaneous T-cell lymphoma (CTCL) and peripheral T-cell lymphoma (PTCL), which Walsh indicates have not been adequately disclosed on the drug warning label.

The claim joins a number of similar Dupixent cancer lawsuits filed in recent weeks, each raising nearly identical allegations that the manufacturers knew or should have known of the risks of CTCL and PTCL, yet placed a desire for profits before consumer safety bty failing to adequately warnings to patients or the medical community.

According to the complaint, Walsh was diagnosed with atopic dermatitis and began receiving Dupixent injections in July 2017 until February 2018, and again from November 2018 to January 2019. At that time, Walsh had never been diagnosed with CTCL.

The lawsuit alleges that Walsh experienced little to no improvement from Dupixent injections and was diagnosed in May 2021 with two forms of cutaneous T-cell lymphoma, mycosis fungoides and Sézary syndrome. By the time of diagnosis, the cancer had already progressed to stage IV.

Since the diagnosis, Walsh has undergone numerous treatments, including radiation therapy and multiple cancer medications. However, she did not discover that Dupixent may have been the cause of the cancer until October 2025, when her healthcare provider first mentioned the potential risk.

Walsh is preparing to undergo stem cell transplant therapy next month, but the lawsuit notes that she could have received treatment earlier, or avoided cancer altogether, if the manufacturers had adequately warned doctors about what to look for.

“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, despite Defendants’ knowledge of same. Defendants also failed to warn Plaintiff and her medical providers to cease use of Dupixent and/or to get appropriate diagnostic tests to diagnose or rule out CTCL if Dupixent did not improve her condition or if her skin condition became worse while on Dupixent.”

– Alison Walsh v. Regeneron Pharmaceuticals Inc. et al

The lawsuit presents claims of failure to warn, negligence, negligent misrepresentation and breach of warranty.

The claim will be closely watched by other former users and Dupixent cancer lawyers reviewing potential claims, as the early management of Walsh’s case could lay the groundwork for how courts handle other lawsuits that may be filed in the coming weeks and months, as more former users learn that Dupixent may have caused CTCl, PTCL or another form of T-cell lymphoma diagnosed in recent years.