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Dupixent MDL Status and Litigation Update

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What Is an MDL and Why It Matters for Dupixent Plaintiffs

Multidistrict litigation (MDL) is a procedural mechanism under 28 U.S.C. § 1407 that allows the Judicial Panel on Multidistrict Litigation to transfer civil actions pending in different federal districts to a single district for coordinated pretrial proceedings. The rationale is efficiency: when hundreds or thousands of cases involve common questions of fact — such as whether Dupixent causes CTCL, whether Sanofi knew of the risk, and whether the label was inadequate — it is wasteful to have each case conduct independent discovery, retain separate experts, and litigate the same Daubert motions in dozens of courtrooms.

For Dupixent plaintiffs, MDL consolidation offers both advantages and risks. The advantages include shared resources: plaintiffs' attorneys pool their expertise and funding through a Plaintiffs' Steering Committee (PSC), conduct unified discovery against Sanofi and Regeneron, and develop common expert reports on general causation, regulatory history, and internal corporate knowledge. The risks include delay: MDL proceedings can take years before bellwether trials begin, and individual plaintiffs cannot unilaterally accelerate their cases. Additionally, the MDL judge's rulings on Daubert and summary judgment apply across all cases, meaning an unfavorable ruling can affect every plaintiff simultaneously.

The Venue Dispute: N.D. Georgia vs. S.D. New York

The choice of MDL venue is one of the most consequential early decisions in mass tort litigation. Plaintiffs in the Dupixent CTCL litigation have proposed the Northern District of Georgia (Atlanta) as the transferee court, citing the district's experienced judiciary, manageable docket, efficient case management history, and geographic accessibility for plaintiffs' counsel. Atlanta's federal courthouse has handled significant pharmaceutical and product liability cases, and the Northern District's local rules facilitate streamlined discovery scheduling.

Sanofi and Regeneron prefer the Southern District of New York, where Regeneron is headquartered in nearby Tarrytown, Westchester County. The defense argument centers on convenience for corporate witnesses and the SDNY's familiarity with complex pharmaceutical litigation. However, plaintiffs counter that housing the MDL in a defendant's home district creates an inherent appearance of favoritism, and that the SDNY's notoriously heavy docket may cause scheduling delays. Other districts mentioned as potential venues include the Eastern District of Pennsylvania (Philadelphia's pharmaceutical MDL pedigree), the District of New Jersey (Sanofi US headquarters), and the Northern District of Illinois (Chicago's experienced mass tort bench).

The JPML will weigh several factors in its venue decision: the convenience of the parties and witnesses, the number of cases already pending in each district, the experience of judges in the candidate districts with pharmaceutical MDLs, and the overall efficiency of the proposed transferee court. The Panel's decision is expected in mid-to-late 2026, and the selected venue will become the procedural home for all federal Dupixent CTCL cases through pretrial completion.

Current Case Count and Filing Trajectory

As of early 2026, over 250 individual Dupixent CTCL lawsuits have been filed in federal courts across at least 15 districts. The filing rate has accelerated following media coverage of the CTCL risk and the announcement of the MDL petition. Legal analysts project the case count could reach 1,000 to 5,000 within 12 to 18 months as attorney advertising drives case acquisition and more Dupixent patients undergo skin biopsies revealing CTCL. The trajectory mirrors early filings in the Zantac and Roundup litigations, both of which grew from hundreds to tens of thousands of cases within two to three years of MDL formation.

The earliest cases — Richardson v. Sanofi (W.D. Tennessee, October 2025), Johnson v. Sanofi (N.D. Illinois, December 2025), and Fraioli v. Sanofi (S.D. Florida, January 2026) — will likely be considered for bellwether selection given their early filing dates and developed factual records. Bellwether trials are test cases selected to gauge jury response and establish settlement values. In pharmaceutical MDLs, bellwether outcomes often determine whether global settlement negotiations proceed and at what range.

What MDL Means for Your Individual Case

If you have filed or plan to file a Dupixent CTCL lawsuit in federal court, MDL consolidation means your case will be transferred to the selected transferee district for pretrial proceedings. You will retain your own attorney, but your case will be managed alongside all other federal cases under the MDL judge's case management orders. Discovery conducted by the Plaintiffs' Steering Committee will benefit all cases — you will have access to internal Sanofi documents, expert reports, and deposition testimony without your individual attorney needing to independently subpoena those materials.

Your case will not go to trial in the MDL unless it is selected as a bellwether. After MDL pretrial proceedings conclude — which typically takes 2 to 4 years — cases that have not settled are remanded (sent back) to their original filing districts for individual trial. However, most pharmaceutical MDLs result in global settlement before remand. The settlement amount for individual cases is typically determined by a settlement grid that scores cases based on injury severity (CTCL stage), duration of Dupixent use, quality of medical documentation, and other factors.

Key Upcoming Milestones

The Dupixent CTCL litigation is in its earliest stages, with several milestones expected in 2026 and 2027. The JPML is expected to issue its MDL transfer order in mid-to-late 2026, selecting the transferee court and judge. Following transfer, the MDL judge will appoint a Plaintiffs' Steering Committee and issue initial case management orders governing discovery schedules, Plaintiff Fact Sheets (PFS), and defendant document production. General causation expert discovery and Daubert proceedings will follow, likely in late 2027 or early 2028. Bellwether trial selection and preparation could begin in 2028, with the first trials potentially in 2029.

For plaintiffs considering filing, the key takeaway is urgency. Statutes of limitations continue to run regardless of MDL status. Filing now ensures your claim is preserved and positions you to benefit from the earliest stages of coordinated discovery. Cases filed before MDL formation may receive preferential consideration for bellwether selection, and early-filing attorneys often play leadership roles on the Plaintiffs' Steering Committee. Waiting does not improve your position — it risks deadline expiration and places you further back in the queue.

State Court Alternatives to MDL

Not all Dupixent CTCL cases must be filed in federal court. Plaintiffs who file in state court are not subject to MDL transfer. State court filing may be strategically advantageous in plaintiff-friendly jurisdictions like Philadelphia (Pennsylvania), Cook County (Illinois), St. Louis (Missouri), or Madison County (Illinois). Several states have their own mass tort coordination mechanisms — California's JCCP, New York's NYCAL model, and New Jersey's Middlesex County mass tort program — that can achieve consolidation benefits without federal MDL transfer.

The choice between federal and state court filing involves strategic considerations that an experienced pharmaceutical liability attorney can evaluate based on the plaintiff's home state, the applicable law, the quality of the state court venue, and the plaintiff's tolerance for the MDL timeline. Some plaintiffs choose to file in state court to maintain more individual control over their case progression, while others prefer the resources and coordination of the federal MDL. Both paths can lead to favorable outcomes; the decision should be made with full awareness of the trade-offs.

FAQ

Frequently Asked Questions

Can Dupixent cause cancer?

The short answer is yes — and the science behind it is alarming. A peer-reviewed study of 19,612 patients found that Dupixent users face a 4.5 times higher risk of developing cutaneous T-cell lymphoma (CTCL) compared to people who never took the drug. To put that in perspective, a 4.5x relative risk is in the same ballpark as the asbestos-mesothelioma association that drove one of the largest mass tort litigations in American history. The proposed biological mechanism is straightforward and troubling. Dupixent blocks two signaling molecules — IL-4 and IL-13 — that are part of the type 2 immune response. Blocking these signals is what makes the drug effective against eczema and asthma. But those same signals appear to play a role in immune surveillance against T-cell malignancies. By suppressing them, Dupixent may release the brakes on pre-malignant T-cell clones that the immune system had been keeping in check. The result: a cancer that literally disguises itself as the disease the drug is supposed to treat. The FDA placed Dupixent on its safety watchlist in March 2025 and escalated to a formal investigation in September 2025 after receiving more than 300 adverse event reports related to lymphoma and blood cancers. As of April 2026, the investigation is ongoing. Regeneron and Sanofi have not added a specific CTCL warning to the Dupixent label.

What is cutaneous T-cell lymphoma, and why is it connected to Dupixent?

Cutaneous T-cell lymphoma is a cancer of the immune system that begins in the skin. Specifically, T-lymphocytes — white blood cells that are supposed to protect you from infections and abnormal cells — become malignant and accumulate in the skin, forming patches, plaques, and eventually tumors. The most common subtype is mycosis fungoides, which can remain indolent for years or progress to Sezary syndrome, an aggressive form where cancer cells circulate through the bloodstream. The connection to Dupixent lies in the drug's mechanism of action. Dupixent works by blocking IL-4 and IL-13 — two signaling molecules that drive type 2 inflammation. But these molecules also appear to play a role in keeping abnormal T-cells under control. When Dupixent shuts down that pathway, it may allow pre-existing T-cell clones with malignant potential to proliferate unchecked. Researchers describe this as an 'unmasking' effect — the cancer was there, but the immune system was holding it back. Dupixent may remove that restraint. The most dangerous aspect of this connection is diagnostic mimicry. Early CTCL looks almost identical to eczema — red, scaly patches on the skin. For a patient taking Dupixent for eczema, new skin lesions are almost always attributed to eczema flares rather than cancer. This can delay diagnosis by months or years, allowing the cancer to progress to stages where treatment options narrow and survival rates drop sharply.

Who qualifies to file a Dupixent lawsuit?

If you took Dupixent for any condition — atopic dermatitis, asthma, chronic sinusitis, COPD, or any other indication — and were subsequently diagnosed with cutaneous T-cell lymphoma (including mycosis fungoides or Sezary syndrome), you may have a valid claim. There is no minimum duration of Dupixent use required. Some reported cases involve patients who developed CTCL after relatively short treatment periods, which is consistent with the unmasking theory: if Dupixent releases the brakes on a pre-existing malignancy, the cancer can manifest quickly. Family members of people who died from CTCL or T-cell lymphoma after Dupixent use may be eligible to file wrongful death claims. You do not need to have stopped taking Dupixent — active patients with a CTCL diagnosis can file while still receiving treatment for their cancer. The key requirements are documentation of Dupixent use (pharmacy records, insurance claims, or medical records), a confirmed CTCL or T-cell lymphoma diagnosis (pathology report with biopsy confirmation), and filing within your state's statute of limitations. A free consultation with a mass tort attorney can determine whether your specific circumstances support a claim. Consultations are confidential, and most Dupixent attorneys work on contingency — fee terms vary by attorney.

What is the current status of Dupixent lawsuits in 2026?

As of April 2026, all federal Dupixent lawsuits alleging cancer injuries have been consolidated into Multidistrict Litigation No. 3180 by the Judicial Panel on Multidistrict Litigation. The MDL is in its earliest procedural stages — the court has appointed a plaintiffs' steering committee, and initial case management orders are being issued. Discovery has not yet begun in earnest, but attorneys expect the first round of document requests to target Regeneron's internal safety data, communications with the FDA, and pharmacovigilance records. No settlements have been reached and no cases have gone to trial. The litigation follows a well-established pattern for pharmaceutical MDLs: after discovery is substantially complete, the court will select bellwether cases for trial. Bellwether verdicts — typically the first three to five cases tried — establish the litigation's settlement value and create pressure for global resolution. This process typically takes two to four years from MDL formation, meaning bellwether trials could begin in 2028 or 2029. Separately, the FDA's formal investigation into Dupixent's cancer risk remains ongoing. Any regulatory action — particularly a boxed warning or label change requiring specific CTCL risk disclosure — would significantly strengthen plaintiffs' cases and could accelerate settlement discussions.

How much could a Dupixent lawsuit be worth?

It is too early to provide specific settlement projections for Dupixent cases because no settlements or verdicts have been reached. But we can look at comparable pharmaceutical cancer litigations to understand the range of possibilities. In the Roundup litigation, individual settlements for non-Hodgkin lymphoma ranged from approximately $100,000 to over $2 million depending on cancer severity and treatment burden. Bayer ultimately paid over $10 billion to resolve approximately 100,000 claims. For Dupixent, case values will likely be stratified by the severity of the CTCL diagnosis. Early-stage mycosis fungoides managed with skin-directed therapies may fall in the $75,000 to $200,000 range. Advanced CTCL requiring chemotherapy, radiation, or targeted biologic therapy could be valued at $200,000 to $1 million. Wrongful death cases and terminal diagnoses — particularly Sezary syndrome and large cell transformation — could exceed $2 million. One factor that may favor Dupixent plaintiffs is the strength of the epidemiological evidence. A 4.5x relative risk is considered highly significant in both medical research and legal causation standards. The Daubert challenge to plaintiffs' expert testimony — often the most contentious phase of pharmaceutical MDLs — may be less of an obstacle than in litigations with weaker statistical associations.

Did Regeneron and Sanofi know about the cancer risk?

This is the central question in Dupixent litigation — and the answer will emerge from discovery as the MDL progresses. What we know publicly is this: adverse event reports linking Dupixent to lymphoma and blood cancers had been accumulating in the FDA Adverse Event Reporting System (FAERS) for years before the formal investigation. The scientific literature on IL-4/IL-13 pathway disruption and immune surveillance against T-cell malignancies was available to Regeneron's and Sanofi's research scientists at the time of approval and throughout the post-market period. Plaintiffs allege that the manufacturers engaged in inadequate pharmacovigilance — that they failed to investigate the cancer signal with the urgency that the data warranted, and that they failed to update the drug's label to warn specifically about CTCL risk. The current Dupixent label mentions the possibility of malignancies in general terms, but does not specifically warn about cutaneous T-cell lymphoma or the diagnostic confusion that arises from prescribing an eczema drug that can cause a cancer mimicking eczema. If discovery reveals internal documents showing that Regeneron or Sanofi were aware of the CTCL signal and chose not to act — or that they deliberately framed CTCL reports as eczema treatment failures in their pharmacovigilance databases — it could dramatically increase both liability and damages, including potential punitive damages.

Can I file a Dupixent lawsuit if I am still taking the drug?

Yes — you do not need to stop taking Dupixent to file a lawsuit. If you have been diagnosed with CTCL or another T-cell lymphoma while using or after using Dupixent, your legal claim exists regardless of whether you continue the medication. The decision to stop or continue Dupixent is a medical decision that should be made with your treating physician, not your attorney. Some patients with severe atopic dermatitis or asthma have no adequate alternative treatments, and stopping Dupixent could cause significant health deterioration. That said, if you have a confirmed CTCL diagnosis, your oncologist will almost certainly recommend discontinuing Dupixent — continuing a drug that may be promoting T-cell malignancy while simultaneously undergoing cancer treatment is medically counterproductive. The important thing is to make this decision in consultation with your medical team, not based on legal strategy.

How is a Dupixent MDL different from a class action?

The distinction matters because it directly affects how much you can recover. In a class action, all members share a single settlement pot — often resulting in relatively small per-person payments. In a multidistrict litigation (MDL), each plaintiff maintains their own individual case with their own specific facts, damages, and potential recovery. The MDL structure simply consolidates the pretrial process — discovery, expert challenges, and procedural motions — before a single judge for efficiency. In MDL No. 3180, your case is uniquely yours. A patient diagnosed with early-stage mycosis fungoides managed with topical therapy will have a different case value than a patient who underwent chemotherapy for Sezary syndrome or whose family filed a wrongful death claim. The MDL process allows the court to handle common legal issues efficiently while preserving each plaintiff's right to individual assessment and compensation based on their specific circumstances. After bellwether trials establish settlement benchmarks, most MDLs move toward global resolution — a structured settlement program in which individual case values are assigned based on severity tiers, treatment burden, and other case-specific factors. Plaintiffs who are unsatisfied with their assigned value retain the right to opt out and pursue individual trial.

What evidence do I need to file a Dupixent lawsuit?

The evidence you need falls into two categories: proof of Dupixent use and proof of cancer diagnosis. For Dupixent use, the strongest evidence includes pharmacy dispensing records showing when you filled your prescriptions, insurance claims showing Dupixent charges, medical records with prescribing notes, and injection logs from your doctor's office or specialty pharmacy. Even partial records are useful — your attorney can subpoena pharmacy records and insurance claim histories to fill gaps. For your cancer diagnosis, the essential document is your pathology report from the skin biopsy that confirmed CTCL or mycosis fungoides. The report should include the histopathological findings, immunohistochemistry results (CD3+, CD4+, loss of CD7/CD26), and ideally T-cell receptor gene rearrangement results confirming clonality. Your oncology treatment records — including staging workups, PET scans, chemotherapy regimens, and radiation plans — document the severity and treatment burden that drive your case value. You do not need to have all of this documentation organized before consulting an attorney. Most mass tort firms have medical record retrieval teams that gather and organize evidence as part of case preparation. The most important step is to preserve what you have — do not discard Dupixent packaging, pharmacy receipts, or medical records.

My doctor says my CTCL is not related to Dupixent. Can I still file?

Yes — and this is more common than you might think. Many treating physicians are not yet aware of the epidemiological data linking Dupixent to CTCL, or they may be reluctant to attribute a rare cancer to a widely prescribed medication. Your doctor's clinical opinion is important for your medical care, but it is not determinative of your legal claim. In mass tort litigation, causation is established through expert testimony from epidemiologists, toxicologists, and oncologists who analyze population-level data and biological mechanisms. The 4.5x relative risk from the 19,612-patient study provides strong statistical support for general causation — the question of whether Dupixent can cause CTCL in the population. Specific causation — whether Dupixent caused your particular CTCL — is then established through expert analysis of your medical records, treatment timeline, and the absence of alternative explanations. An expert who reviews your chart and finds that you had no CTCL risk factors before Dupixent use, developed CTCL during or after treatment, and had a clinical presentation consistent with drug-induced T-cell lymphoma can provide a compelling specific causation opinion regardless of what your treating physician believes.

Should I stop taking Dupixent if I am worried about cancer?

This is a medical decision, not a legal one — and it should be made in consultation with your prescribing physician. Abruptly stopping Dupixent can cause severe rebound flares of atopic dermatitis or worsening of asthma that may require emergency treatment. Your doctor can evaluate your individual risk factors, discuss the emerging safety data, and consider whether alternative treatments are appropriate for your situation. What we do recommend is vigilance. If you are currently taking Dupixent, discuss the CTCL risk with your dermatologist and ask about a monitoring protocol. Any new or changing skin lesions — particularly patches that look different from your usual eczema, lesions in unusual locations like the buttocks or trunk, or skin changes that do not respond to standard eczema treatments — should prompt a biopsy rather than an assumption that it is just another flare. Early detection of CTCL, if it develops, dramatically improves outcomes. If you are diagnosed with CTCL, your oncologist will almost certainly recommend stopping Dupixent immediately. At that point, the medical and legal decisions align: you need cancer treatment, and continuing a drug suspected of promoting that cancer serves no purpose.

How long will the Dupixent lawsuit take to resolve?

Pharmaceutical MDLs are not quick — and anyone promising a fast resolution is not being honest. Based on the typical trajectory of comparable pharmaceutical cancer MDLs, the Dupixent litigation will likely follow this general timeline: 2026 to 2027 for discovery and expert development; 2027 to 2028 for Daubert challenges (where the court decides whether plaintiffs' and defendants' expert witnesses may testify); and 2028 to 2029 for bellwether trials — the first cases to go to trial. If bellwether verdicts favor plaintiffs, global settlement negotiations typically follow within 12 to 18 months. The realistic expectation for most plaintiffs is a resolution timeline of three to five years from the date of MDL formation — meaning 2029 to 2031 for the bulk of cases. Some cases may resolve sooner if early bellwether results are strongly in plaintiffs' favor and the defendants choose to negotiate rather than face repeated trial losses. The Roundup litigation, for comparison, produced its first plaintiff verdict in 2018 and Bayer announced a $10 billion settlement framework in 2020 — a two-year bellwether-to-settlement cycle. Early filing matters because cases filed early are most likely to be considered for bellwether selection, and bellwether plaintiffs often receive the highest individual recoveries. Filing early also ensures that your evidence is preserved, your medical records are secured, and your case is well-developed by the time settlement discussions begin.
Related Topics

Related Pages

CTCL Diagnosis After Dupixent Use

Cutaneous T-cell lymphoma is a rare and aggressive blood cancer that masquerades as eczema, psoriasis, and other benign skin conditions — making it uniquely dangerous for Dupixent patients who already carry dermatitis diagnoses. Misdiagnosis rates exceed 40 percent in early-stage CTCL because the symptoms overlap so precisely with the conditions Dupixent is prescribed to treat. Dermatologists expect itchy, red patches in their Dupixent patients; what they may not expect is that those patches now harbor malignant T-cells. Staging ranges from IA (limited patches) to IVB (visceral organ involvement and blood-borne Sezary cells), and the difference between a Stage IA diagnosis and a Stage IIB diagnosis can mean the difference between a normal life expectancy and a five-year survival rate below 40 percent. The critical diagnostic tool is a skin biopsy with immunohistochemistry, which can reveal hallmark Pautrier microabscesses — clusters of malignant T-cells in the epidermis that do not appear in benign dermatitis. Every Dupixent patient whose skin condition worsens, changes character, or fails to respond to continued treatment should demand a biopsy, not another refill.

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Dupixent Eye Problems and Ocular Side Effects

Conjunctivitis is the most common adverse event associated with Dupixent, occurring in approximately 30 percent of atopic dermatitis patients in clinical trials — a rate ten times higher than placebo. But conjunctivitis is just the visible surface of a broader ocular toxicity profile that includes blepharitis, keratitis, dry eye syndrome, limbal stem cell deficiency, and in rare but devastating cases, corneal perforation requiring emergency surgical intervention. These eye problems often develop within the first three months of treatment and can persist even after Dupixent is discontinued. Sanofi and Regeneron have acknowledged conjunctivitis on the Dupixent label but have minimized the severity spectrum, leading patients and prescribers to underestimate the risk of serious, vision-threatening complications. For patients who have suffered permanent vision impairment, corneal scarring, or required corneal transplantation due to Dupixent-related ocular injury, the manufacturer's characterization of these events as manageable side effects is contradicted by their clinical experience.

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Dupixent Pediatric Use and CTCL Risk in Children

Sanofi and Regeneron have aggressively expanded Dupixent's pediatric indications, securing FDA approval for atopic dermatitis in children as young as 6 months old in 2022, following earlier approvals for ages 6 to 11 in 2020 and adolescents aged 12 to 17 in 2019. This expansion exposed millions of children with developing immune systems to a biologic drug that blocks IL-4 and IL-13 — cytokines critical to immune maturation, T-cell differentiation, and tumor surveillance. While CTCL is rare in children overall, the long-term consequences of sustained immune modulation during critical developmental windows are unknown because Sanofi's pediatric trials were not designed to detect rare cancers and follow-up periods were insufficient to capture latent malignancies. Pediatric Dupixent claims carry unique urgency: children have longer remaining lifespans over which to develop delayed-onset lymphoma, the immune insult occurs during a period of rapid lymphocyte development, and parents made treatment decisions based on safety assurances that did not account for the emerging CTCL signal. The duty to warn is heightened for pediatric drugs because parents — not the patient — make the consent decision, and they deserve complete risk information to exercise informed judgment.

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Dupixent Wrongful Death Claims

When cutaneous T-cell lymphoma caused by Dupixent progresses to advanced stages and the patient dies, surviving family members may pursue wrongful death and survival action claims against Sanofi and Regeneron. Richardson v. Sanofi, filed in October 2025 in the Western District of Tennessee, was one of the first named Dupixent CTCL lawsuits and involved allegations of fatal lymphoma progression. Wrongful death claims compensate the decedent's family for loss of companionship, financial support, and funeral expenses, while survival actions compensate the decedent's estate for the pain, suffering, and medical costs the patient endured before death. These are legally distinct claims with different standing requirements, damage calculations, and statutes of limitations. State law controls who may bring a wrongful death claim — in some states, only a surviving spouse or children have standing, while in others, parents, siblings, or domestic partners may also qualify. The interplay between wrongful death statutes and product liability discovery rules creates filing deadline complexities that can extinguish viable claims if not handled promptly.

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Parent Case

Dupixent Lawsuit Lawsuit

Dupixent (dupilumab) is a monoclonal antibody biologic drug developed by Regeneron Pharmaceuticals and marketed jointly with Sanofi-Aventis and its subsidiary Genzyme Corporation. The FDA first approved Dupixent in March 2017 for adults with moderate-to-severe atopic dermatitis (eczema) who had not responded adequately to topical treatments. Subsequent FDA approvals expanded its use to moderate-to-severe asthma in October 2018, chronic rhinosinusitis with nasal polyps (CRSwNP) in June 2019, eosinophilic esophagitis (EoE) in May 2022, prurigo nodularis in September 2022, and chronic obstructive pulmonary disease (COPD) with an eosinophilic phenotype in September 2024. With more than 37 million prescriptions dispensed globally, Dupixent became one of the best-selling biologic drugs in the world, generating over $13 billion in annual revenue for its manufacturers. The drug works by inhibiting interleukin-4 (IL-4) and interleukin-13 (IL-13) signaling — two cytokines that drive type 2 inflammation. While this mechanism was considered targeted and relatively safe, post-market surveillance and independent research have identified a concerning association between Dupixent use and cutaneous T-cell lymphoma (CTCL). CTCL is a rare cancer in which T-cells become malignant and attack the skin, often presenting initially as rashes or patches that can be mistaken for eczema. The critical concern is that symptoms of CTCL closely mimic the very conditions Dupixent is prescribed to treat, potentially masking the cancer and delaying diagnosis. A peer-reviewed study analyzing 19,612 patients found that Dupixent users faced a 4.5 times higher risk of developing CTCL compared to patients not using the drug. The FDA placed Dupixent on its drug safety watchlist in March 2025 and escalated to a formal investigation in September 2025 after receiving over 300 adverse event reports related to lymphoma and blood cancers. As of February 2026, individual lawsuits are being filed against Regeneron Pharmaceuticals, Sanofi-Aventis, and Genzyme Corporation. Plaintiffs allege that the manufacturers knew or should have known about the cancer risk and failed to adequately warn patients and prescribing physicians. Specific allegations include failure to warn, defective design of the drug's labeling, negligence in post-market surveillance, and fraudulent concealment of safety data. A wrongful death suit was filed in Tennessee in October 2025 on behalf of Chandra Richardson. Additional cases have been filed in Florida (January 2026) and Illinois (December 2025). Legal experts anticipate that the Judicial Panel on Multidistrict Litigation will consolidate federal cases into an MDL within the next 12 months.

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