These Dupixent Cases Involving T-cell Lymphoma Cancer Are Against Regeneron Pharmaceuticals and Sanofi-Aventis

We are currently investigating possible Dupixent lawsuits for patients who were diagnosed with a relatively rare cancer, T-cell lymphoma, after they started using Dupixent (dupilumab).

These Dupixent lawsuits would be filed against the pharmaceutical companies Regeneron Pharmaceuticals, Inc., and Sanofi-Aventis U.S. LLC, based on various allegations of legal liability concerning the potential increased risk of T-cell lymphoma.

We begin with the medical aspect of these Dupixent lawsuits, which are being filed on behalf of patients. Generally, the cases allege that Dupixent caused the development and/or aggravation of their T-cell lymphoma.

As background, here is some basic T-cell lymphoma explanatory information:

• T-cell lymphoma affects white blood cells called T cells or T lymphocytes. T-cells help the body’s immune system to fight germs.
• T-cell lymphomas are a subtype of non-Hodgkin lymphoma (NHL).
• There are several types of T-cell lymphoma, including cutaneous T-cell lymphoma (CTCL) and peripheral T-cell lymphoma (PTCL).
• CTCL is a T-cell lymphoma that starts in the skin, whereas PTCL refers to systemic T-cell lymphomas that are found in the lymph nodes, other organs, and the blood. Also, some types involve the skin.
• Mycosis fungoides and Sézary syndrome are the two most common subtypes of CTCL.

We turn next to the legal aspects of these Dupixent lawsuits against Regeneron and Sanofi. Essentially, it is alleged that these Defendants failed to warn patients and their doctors about an increased risk of development and/or exacerbation of T-cell lymphoma, including CTCL and PTCL.

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Significantly, the U.S. Prescribing Information document, or “drug label”, for Dupixent (accessed 10/6/25) [PDF, 71 pages] does not have any warning or any information concerning an association between Dupixent and the development or exacerbation of T-cell lymphoma, including CTCL and PTCL.

In more detail, the legal liability allegations that might be presented in personal injury or wrongful death Dupixent lawsuits include, but are not limited to:

• Defendants Regeneron and Sanofi knew or should have known of the potential of Dupixent to exacerbate or accelerate pre-existing T-cell lymphoma, including CTCL and PTCL, or increase susceptibility to its development.
• Defendants failed to adequately test Dupixent to investigate the risks, including the potential of exacerbating pre-existing T-cell lymphoma or increasing susceptibility to its development.
• Defendants failed to warn physicians and patients that Dupixent should not be prescribed or administered to patients with confirmed or suspected T-cell lymphoma, including CTCL and PTCL.
• Defendants failed to warn physicians and patients that the use of Dupixent in patients with adult-onset atopic dermatitis and no history of atopy may result in the development and/or acceleration of CTCL and PTCL.

In summary, these Dupixent lawsuits against Regeneron and Sanofi are based on their wrongful conduct in connection with the development, testing, labeling, packaging, promotion, advertising, marketing, distribution, and selling of Dupixent (dupilumab).

For more, you can take a look at our September 26, 2025, article, “Dupixent Drug Injury Lawsuits For Patients Diagnosed With CTCL Cancer“.

If we can assist you with a possible Dupixent lawsuit, feel free to submit a Drug Injury Case Evaluation Form online or call 910-256-2971 to discuss your case with attorney Tom Lamb.

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