Background
Eylea (aflibercept) is Regeneron Pharmaceuticals’ blockbuster ophthalmic treatment for macular degeneration and diabetic retinopathy, generating billions of dollars in annual revenue. When Amgen received FDA approval for PAVBLU, its aflibercept biosimilar, in August 2024, Regeneron filed patent infringement litigation to block commercial entry. The litigation was centralised as a multidistrict proceeding before Judge Kleeh in the Northern District of West Virginia.
Amgen mounted an aggressive defence that went beyond validity challenges: it filed antitrust counterclaims under the Walker Process doctrine. The Walker Process theory, dating to the 1965 Supreme Court case Walker Process Equipment v. Food Machinery, allows a defendant to sue for antitrust violations when a patent holder obtained its patent through knowing fraud on the USPTO and then attempted to enforce that fraudulently obtained patent. Amgen alleged that Regeneron had made false inventorship declarations and other material misstatements to the USPTO in obtaining U.S. Patent No. 12,331,099, which is the primary patent blocking PAVBLU’s entry.
The Court’s Holding
Judge Kleeh dismissed Amgen’s Walker Process antitrust counterclaims and California Unfair Competition Law claims. To survive dismissal, Amgen needed to plausibly allege that Regeneron had knowingly made false statements to the USPTO—not merely that the patent may be invalid or that prosecution mistakes were made. Amgen failed to plead the required “knowing” element with sufficient specificity: its pleading alleged irregularities in the inventorship declarations but did not establish that Regeneron knew those declarations were false at the time they were submitted.
The Walker Process doctrine requires more than ordinary inequitable conduct; it requires a deliberate, knowing scheme to obtain a patent through fraud. Courts apply rigorous pleading standards to these claims precisely because permitting every accused infringer to file antitrust counterclaims based on arguable prosecution errors would chill legitimate patent enforcement. Without plausible allegations of scienter, the antitrust claims could not proceed.
The court retained Amgen’s laches defence—the argument that Regeneron unreasonably delayed bringing suit—which will continue in the litigation. The patent infringement claims on the merits are not affected by this ruling and will proceed toward trial.
Key Takeaways
- Walker Process antitrust counterclaims require pleading that the patent holder knowingly committed fraud on the USPTO—mere allegations of prosecution irregularities, mistakes, or an invalid patent are insufficient.
- Courts apply heightened pleading scrutiny to Walker Process claims to prevent accused infringers from reflexively converting every patent dispute into an antitrust case.
- Biosimilar entrants who want to use the Walker Process theory must conduct thorough pre-filing diligence to document specific knowing misstatements in prosecution—vague allegations of inventorship issues will be dismissed.
- Laches (delay in filing suit) survived as a defence, which could limit Regeneron’s damages or relief if proved at trial.
Why It Matters
The pharmaceutical biosimilar landscape is the highest-stakes battleground in modern patent law. Each month of blocked market entry for a biosimilar drug like PAVBLU can translate into billions of dollars of sales for the incumbent originator—and billions in savings withheld from patients and healthcare systems. Biosimilar developers have increasingly turned to Walker Process antitrust theories as a way to both challenge blocking patents and seek affirmative relief for the market harm caused by asserting fraudulently obtained patents.
This ruling underscores the doctrinal difficulty of that strategy: Walker Process requires proving not just an invalid patent but a deliberately fraudulent one. For Amgen and other biosimilar developers, the path to antitrust relief runs through careful factual development of specific prosecution misconduct—not just legal argument about the patent’s validity. The case will continue on the merits of the infringement and validity disputes, making it one of the more significant ongoing Hatch-Waxman proceedings in the country.
Surfaced via Law360 IP.