Dupixent Side Effects Caused CTCL, Tumors, Lawsuit Alleges

Lawsuit claims plaintiff would have never risked reigniting his CTCL had he or his doctor been accurately informed of Dupixent side effects.

A Louisiana man has filed a product liability lawsuit blaming the eczema drug Dupixent for causing a rare form of cancer he once thought he had beaten to return, along with new tumors and other health problems.

Sidney Michael Lewis brought the complaint (PDF) in the U.S. District Court for the District of New Jersey on August 20, naming Regeneron Pharmaceuticals Inc., Sanofi-Aventis U.S. LLC and Genzyme Corporation, Dupixent’s manufacturers, as defendants.

Lewis claims the companies have failed to provide adequate warnings to the medical community and patients that Dupixent side effects can cause, or reignite, a rare form of T-cell lymphoma. Instead, he says they fraudulently marketed the drug as safer than it actually is.

Dupixent Side Effects

Dupixent (dupilumab) was approved by the U.S. Food and Drug Administration (FDA) in 2017 for the treatment of atopic dermatitis, a form of eczema. Since then, the drug has received numerous additional approvals to promote it 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, the manufacturers and FDA have seen an increasing number of reports linking Dupixent side effects to patients developing a form of T-cell lymphoma known as cutaneous T-cell lymphoma (CTCL) that primarily affects the skin. According to patient reports, the drug can also cause patients already diagnosed with CTCL to experience a flare up or recurrence of their cancer.

As a result, the drugmakers now face a growing number of Dupixent cancer lawsuits in federal courts nationwide, each alleging 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 CTCL Side Effect Allegations

According to the complaint, Lewis was originally diagnosed with stage 1 cutaneous T-cell lymphoma in early 2017, the same year Dupixent was first approved. In 2019, doctors identified his CTCL as a form of mycosis fungoides, the most common form of CTCL. Lewis claims he underwent a variety of cancer treatments at the time, including bexarotene, praluent, methotrexate with folate supplementation, photo/light therapy and topical triamcinolone.

In March 2025, Lewis was prescribed Dupixent for the treatment of his eczema. He was once again diagnosed with CTCL in October 2025, along with large cell transformation, increased number of CD30-positive cells and new tumors. He says that he ceased using Dupixent that November.

The lawsuit notes that if Lewis or his doctor had been informed that Dupixent could cause his CTCL to return, they would have used another treatment to address his eczema. However, Lewis argues the manufacturers knew of the potential for CTCL side effects and hid the true risks of Dupixent to protect their profit margins.

“Despite its historical infrequence in the population, CTCL has been widely reported among patients taking Dupixent. These cases have included diagnoses of new, primary CTCL as well as an unexpected ‘unmasking’ or severe and rapid clinical progression of otherwise subclinical and undiagnosed CTCL occurring weeks to years following initiation of Dupixent use. Evidence supporting a causal relationship between use of Dupixent and incident CTCL is derived from both experimental and observational studies in humans.”

– Sidney Michael Lewis v. Regeneron Pharmaceuticals Inc. et al.

Lewis’s doctors have told him that he will likely require medical treatment and monitoring for CTCL for the rest of his life. The lawsuit presents claims of failure to warn, negligence, fraudulent misrepresentation, negligent misrepresentation and breach of warranty. It seeks both compensatory and punitive damages.

Dupixent CTCL Lawsuits

The complaint will be folded into a Dupixent CTCL lawsuit multidistrict litigation (MDL) in the District of New Jersey before U.S. District judge Zahid N. Qurashi, who is overseeing coordinated discovery and pretrial proceedings for the consolidated claims.

Dupixent lawyers anticipate the judge will direct attorneys to prepare several cases representative of the majority of the litigation to serve as “bellwether” trials. These early test trials are designed to provide an opportunity to see how juries respond to the strengths and weaknesses of arguments and evidence.

Although not binding on other claims, the bellwether trial outcomes 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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