Lawsuit Alleges Dupixent Caused Mycosis Fungoides Diagnosis

Manufacturers allegedly failed to properly test Dupixent injections before they were placed on the market, putting patients’ health at risk.

According to a new product liability lawsuit, three years of receiving Dupixent injections left a Massachusetts man with a rare form of cancer that attacks the immune system.

Andrew Zaikis filed the complaint (PDF) in the U.S. District Court for the District of New Jersey on July 10, naming Regeneron Pharmaceuticals Inc. and Sanofi-Aventis U.S. LLC, Dupixent’s manufacturers, as the defendants.

The lawsuit accuses the manufacturers of failing to properly test the drug before it was released on the market, which could have revealed the injections’ link to cancer risks. Zaikis alleges that the companies placed profit before patient safety, rushing the drug to market without adequate safety warnings.

Dupixent Cancer Risks

Dupixent (dupilumab) was first approved by the U.S. Food and Drug Administration (FDA) in March 2017 for the treatment of atopic dermatitis, a form of eczema. Since then, the agency has expanded approvals for the drug, allowing it to be marketed as a treatment for inflammatory conditions affecting the skin and respiratory system, including asthma, chronic obstructive pulmonary disease, or COPD, and other conditions involving overactive immune responses.

However, the FDA has received an increasing number of reports from patients who indicate Dupixent side effects caused them to develop cutaneous T-cell lymphoma (CTCL), a form of T-cell lymphoma related to non-Hodgkin’s lymphoma that primarily affects the skin. The two most common forms of CTCL are mycosis fungoides and Sézary syndrome.

Due to the cancers similarity to many of the conditions Dupixent is designed to treat, like itchy, rashy skin, doctors can have difficulty making the proper diagnosis. In some instances, patients report they continued receiving Dupixent as the disease progressed because neither the patients nor the medical community were made aware of the potential cancer risks.

The reports have led to a growing number of Dupixent cancer lawsuits being filed in courts nationwide. Many of the cases involve claims that Regeneron and Sanofi-Aventis failed to provide proper instructions to doctors or alert them to the need for medical monitoring to detect early signs of cancer development.

Dupixent Mycosis Fungoides Diagnosis

Zaikis’s lawsuit indicates he began receiving Dupixent injections in October 2022. He continued to receive the shots every two weeks until discontinuing the drug in January 2026.

In November 2025, Zaikis developed an itchy rash, which continued to worsen until January, when his doctor took him off the drug. The next month Zaikis was diagnosed with mycosis fungoides, which is the most common form of CTCL.

The complaint alleges that the manufacturers knew, or should have known, about the potential cancer risks, which can exacerbate or accelerate pre-existing T-cell lymphoma, in addition to causing new diagnoses.

Zaikis indicates the companies ignored evidence from peer-reviewed reports, case studies, epidemiologic articles and other scientific evidence linking Dupixent to increased cancer risks.

“Numerous case reports and scientific studies have established that Dupixent causes T-cell lymphoma, including CTCL, and/or accelerates its progression. Defendants failed to warn, instruct, advise, educate, or otherwise inform Dupixent users and prescribers, including Plaintiff and Plaintiff’s treating physicians, about the risk of development and/or exacerbation of CTCL. The U.S. label for Dupixent makes no mention of these risks.”

– Andrew Zaikis v. Regeneron Pharmaceuticals et al.

Zaikis’s CTCL diagnosis has resulted in severe physical and emotional injuries, loss of enjoyment of life, mental and physical pain and suffering and medical expenses. He presents claims of breach of warranty, violation of the New Jersey Product Liability Act and negligence, seeking both punitive and compensatory damages.

Dupixent Cancer Lawsuits

As one of a number of similar Dupixent cancer lawsuits, Zaikis’s complaint will be consolidated with other claims filed in federal courts nationwide as part of a Dupixent multidistrict litigation (MDL) based in the District of New Jersey before U.S. District Judge Zahid N. Quraishi, who is overseeing coordinated discovery and pretrial proceedings.

The judge is eventually expected to direct attorneys to prepare several cases representative of the litigation as a whole to serve as “bellwether” trials. These early test trials are meant to provide an opportunity to see how juries respond to the strengths and weaknesses of the plaintiffs’ and defendants’ arguments and evidence.

While not binding on other claims, the bellwether results could help attorneys negotiate a global Dupixent cancer lawsuit settlement. However, if the litigation is not resolved after pretrial proceedings and selected cases are completed, Judge Quraishi is expected to remand the remaining claims to their originating federal court districts for individual trials.

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