The first case management conference for the federal multidistrict litigation against Sanofi and Regeneron opened this past Friday. The proceedings address allegations that the drug Dupixent (dupilumab) can cause, accelerate, or unmask cutaneous T-cell lymphoma (CTCL). Weitz & Luxenberg, representing the largest group of plaintiffs, appeared at the hearing led by Judge Zahid N. Quraishi of the U.S. District Court for the District of New Jersey.

The litigation centers on claims that patients and physicians were not adequately warned about the risk of CTCL development or progression while using Dupixent. Laura Baughman, a partner at Weitz & Luxenberg leading the firm’s Dupixent litigation, stated that Sanofi’s own educational materials for doctors describe how this cancer can be mistaken for eczema and unmasked by the drug. She emphasized that if the company understood this risk, clear warnings were warranted, noting that the U.S. label still does not include a lymphoma warning.

Regulatory and scientific context

CTCL is a rare cancer of the immune system that initially appears on the skin. In its early stages, it can look almost identical to eczema, the primary condition Dupixent is prescribed to treat. The lawsuits allege that Sanofi and Regeneron failed to disclose the potential link between Dupixent use and CTCL.

In March 2025, the FDA identified CTCL as a potential signal of serious risk associated with Dupixent based on its adverse event reporting system. Additionally, a 2024 study published in the Journal of the American Academy of Dermatology found significantly higher odds of CTCL among eczema patients treated with Dupixent compared to those not treated. Sanofi has maintained that the scientific literature does not support a causal association.

Litigation timeline and claims

The initial case management conference took place one year to the day after Weitz & Luxenberg and co-counsel filed the first Dupixent lawsuit. Ellen Relkin, chair of Weitz & Luxenberg’s Drug and Medical Device Litigation practice group, stated that people were told their rash was eczema while a cancer progressed. She noted that the litigation focuses on what the companies knew, when they knew it, and why patients never heard about the risks.

Patients are advised not to stop taking any prescribed medication without consulting their doctor. Individuals diagnosed with CTCL, mycosis fungoides, or Sézary syndrome after using Dupixent are encouraged to seek further information through legal channels.

What the numbers show

The divergence between regulatory signals and labeling actions is a key point of contention. While the FDA flagged CTCL as a potential signal of serious risk in March 2025 and peer-reviewed studies reported higher odds of CTCL in treated patients, the drug’s U.S. label remains unchanged regarding lymphoma warnings. This gap between identified risk signals and consumer-facing disclosures forms the core of the plaintiffs' argument regarding negligence and failure to warn.

Sanofi SA and Regeneron Pharmaceuticals have expanded their two-decade-long antibody partnership to jointly develop next-generation treatments. Sanofi will deliver a $1 billion upfront payment to secure the expanded license and collaboration agreement.

The new contract outlines the potential for Regeneron to earn up to an additional $7 billion through development, regulatory, and commercial milestone payouts. This move builds upon the success of Dupixent, which saw sales rise 37.6% to €5.154 billion in Q2.

Financial structure and cost sharing

Under the updated alliance, both companies will divide development and commercialization expenses for the new therapeutic programs equally. They will also share future profits from these prospective products on a 50:50 basis worldwide. The existing profit-sharing structure for Dupixent remains unchanged.

Pipeline expansion targets

The partners will co-develop four novel long-acting antibodies invented by Regeneron. These candidates target specific interleukins, including IL-13, IL-4xIL-13 bispecific, IL-4, and IL-4Rα.

• REGN20423: A Phase 1 trial initiated in May 2026 evaluates this IL-13 antibody. The study expects to enroll roughly 144 subjects and conclude in 2028.
• Other Candidates: Three additional candidates are expected to enter clinical studies in 2027.

Strategic context

Sanofi CEO Belén Garijo stated that Dupixent sales are now expected to reach around €25 billion in 2030, complemented by approximately €10 billion from other Pharma launches. The French biotech signaled a tougher approach to research and development, noting that recent pipeline setbacks reflected weaknesses in decision-making rather than scientific capabilities.

What the numbers show

The deal structure highlights a shift toward risk-sharing in high-value biotech collaborations. By splitting costs and profits 50:50 for new programs, both entities align incentives for long-term success while leveraging the existing cash flow from Dupixent. The $1 billion upfront payment represents a significant immediate capital outlay for Sanofi, balanced against the potential $7 billion in future milestone payments tied to regulatory and commercial success.