Dupixent Deep Dive

CTCL is one of those diseases that sounds obscure until you realize how perfectly it fits into the Dupixent s why diagnosis is often a saga—multiple biopsies, T-cell receptor studies, sometimes months or years of uncertainty before a pathologist finally calls it what it is. Some patients have the slow-burn version, mycosis fungoides, which can smolder for years. Others develop Sézary syndrome, the aggressive, blood-involved variant with a median survival measured in a handful of years. Treatments reflect that t behave like other cancers—chronic for some, devastatingly fast for others.

What woke up the plaintiff bar? Two large, peer-reviewed studies from 2024 and 2025 indicate that patients treated with Dupixent developed CTCL at roughly four times the rate of similar patients who never took the drug. The elevated signal shows up across multiple datasets, including some asthma cohorts, where lymphoma appears more frequently in Dupixent users than in patients using other biologics. No one loves talking about proportional-reporting ratios, but the CTCL signal has logged enough FDA Adverse Event Reporting System (FAERS) entries to draw FDA attention—which is how Dupixent ended up on the agency’s “Potential Signals of Serious Risks” list this year.

Now, what does this mean in practice for plaintiff firms, marketers, and anyone deciding whether to plant a Dupixent flag in their 2026 mass-torts portfolio?

Start with the size of the potential pool. Dupixent has more than a million active users across its approved indications. CTCL itself is rare—1,000 to 1,500 new U.S. cases per year—but when you apply the emerging risk ratios to a medication taken by such a massive population, you don’t need sky-high rates to get meaningful litigation numbers. If even a modest single-digit percentage of CTCL diagnoses in Dupixent users end up linking the cancer to the drug, you’re potentially looking at hundreds of viable claimants nationwide, even more if the FDA issues a formal warning. That’s not Zantac or talc volume. It’s more like a focused oncology MDL—lean, serious, and potentially high-value.

And value is where this docket gets interesting. CTCL is not a “soft-tissue injury.” It’s a chronic, often life-limiting cancer with painful treatments, risk of progression to systemic disease, and massive quality-of-life burdens. Early discussions among plaintiff lawyers suggest six-figure baseline settlement values for early-stage cases (think $150k–$300k), high six figures for moderate disease requiring systemic therapy ($300k–$700k), and seven figures for aggressive or fatal CTCL. There are cases. There are damages. This looks like it could be a real case.

But this will not be an “easy intake” litigation. This is not hair relaxer, where screening forms can run on autopilot. CTCL cases require pathology. Real biopsies. Treatment histories. Year-over-year dermatology records. Timing matters, diagnosis matters, and the ability to prove that Dupixent preceded the cancer—not just coexisted with a misdiagnosed one—is the difference between a viable lawsuit and a dead end. Plaintiff firms already hint that they’re being choosy, focusing on clients with clear post-Dupixent diagnoses rather than diffuse “my rash got worse” complaints. The lead funnel here won’t be a flood—it’ll be a sift. Expect high acquisition cost, high screening cost, and potentially high payout.

The biggest wildcard? Daubert. This case will stand or fall on causation experts. The defense is going to push the idea that CTCL was always there, that Dupixent merely unmasked an existing malignancy, and that atopic dermatitis itself carries an elevated CTCL risk independent of any drug exposure. Plaintiffs will counter with the risk differentials, mechanistic theories around IL-4 and IL-13 modulation, and cases where disease morphology changed dramatically only after Dupixent began.

This is not a simple epidemiology fight; it’s a subtle one, with immunology and dermatopathology intertwined. If this becomes an MDL—and it very likely will if filings hit even a few hundred cases—the first major inflection point will be a Daubert ruling on general causation, probably 2–3 years after consolidation.

So let’s talk timing. Right now, we’re in the “early chatter” phase—individual cases filed, dozens of national firms launching investigations, and growing awareness that the FDA may eventually act. Most recently, on October 1, 2025, a wrongful-death lawsuit in Tennessee alleged that a woman began Dupixent, was diagnosed with CTCL soon after, and died within months—turning a theoretical safety concern into a live, high-stakes case.

If filings pick up through 2026, a petition to the JPML could land anywhere from late 2026 to mid-2027, with centralization shortly thereafter. Add eighteen months for discovery and expert challenges, and you’re probably looking at 2029 as the earliest window for initial bellwethers. Sanofi and Regeneron are not early settlers. They’re the kind of defendants who pour sugar in the gas tank of any mass tort they don’t think you can prove — and Dupixent, with its complicated immunology, is exactly the kind of case they believe they can win on science.

That makes Dupixent, oddly enough, a perfect Thanksgiving metaphor: it’s the dish that isn’t the centerpiece yet, but everyone keeps going back for “just one more look.” It’s early, but the ingredients for a meaningful mass tort are already laid out—the enormous patient population, the rare but devastating injury, the FDA signal, the emerging literature, the big-firm attention, and the money numbers that make litigation sustainable for both plaintiffs and defendants.

If the science continues to break this way, Dupixent could easily become the mass-tort equivalent of the post-dessert football game: no one planned their holiday around it, but everyone suddenly cares who’s winning. And for firms that get in early—carefully, with real screening protocols and serious experts—it might be the most profitable dish on the table.  Happy Thanksgiving!