Federal Circuit Reaffirms 'By Another' Standard Under Pre-AIA Law In Patent Dispute Over Merck Serono's MS Drug Highlights

Highlights

• On Oct. 30, 2025, the U.S. Court of Appeals for the Federal Circuit issued a precedential decision in Merck Serono S.A. v. Hopewell Pharma Ventures, Inc., clarifying how “by another” prior art determinations should be made under pre-America Invents Act (AIA) patent law.
• The AIA was a major patent reform law enacted in 2011 that made significant changes to U.S. patent law, most notably by switching from a "first to invent" system to a "first inventor to file" system.
• The Court reaffirmed that for a reference to be excluded as prior art, the inventive entity must be exactly the same — a simple overlap of inventors is not enough.

Background

The case involved a dispute over Merck's patents on oral dosing regimens of cladribine for treating multiple sclerosis. Hopewell Pharma challenged the validity of these patents in inter partes review, arguing that prior art references — including a patent application by Bodor and a publication by Stelmasiak — rendered Merck's claims obvious. Merck contended that these references should not qualify as prior art under pre-AIA law because they were created by Merck inventors or their collaborators, not "by another party."

A key dispute was whether the Bodor reference qualified as prior art "by another" under pre-AIA 35 U.S.C. § 102(a) and (e). Merck argued that one of its patent inventors had also contributed to the earlier Bodor application, and thus the reference should not count as prior art. This commonly arises in collaborative research settings where inventors work on related projects and publications overlap.

To overcome the "by another" hurdle, Merck needed to prove — using objective and corroborated evidence — that all named inventors of the Merck patent were also the inventive entity behind the Bodor reference. In practice, this means supplying contemporaneous documentation such as laboratory notebooks, dated emails, research data, meeting notes, or invention disclosure forms that clearly establish contributions to conception for each inventor.

The Patent Trial and Appeal Board (PTAB), and ultimately the Federal Circuit, found that Merck failed to provide sufficient evidence to show identical inventive entities. As a result, the Bodor reference was treated as prior art and, combined with Stelmasiak, used to invalidate Merck's patent claims as obvious.

Key Takeaway from the Statute: The "By Another" Rule

Under pre-AIA 35 U.S.C. § 102(a) and § 102(e), a patent is not granted if the invention was previously disclosed or described "by another" before the applicant's invention. The law strictly requires that, for a prior disclosure to be excluded as prior art, the inventive entities must be identical; overlapping inventors are not enough. Proof of inventorship — shown through solid supporting records — is crucial to meeting this legal standard.

Practical Implications

The Merck Serono decision underscores the importance of establishing clear inventorship from the outset. Companies and patent practitioners should consider the following best practices:

• Diligent Recordkeeping: Maintain detailed, contemporaneous records (e.g., lab notebooks, dated drafts, meeting notes, emails) documenting each team member's contributions to inventive projects.
• Inventorship Audits:  Periodically review project documentation and inventor lists for all patent applications, especially when preparing continuations, divisionals, or new filings following collaborative research.
• Collaboration Agreements:  Define procedures and responsibilities around inventorship tracking in joint research or sponsored study contracts.
• Dispute Readiness: If challenged, be prepared to supply clear, corroborated evidence of inventorship from the time the invention was mad— not just after the fact.

Bottom Line

The Federal Circuit's ruling underscores the strictness of the "by another" rule for pre-AIA patents: only references with the exact same group of inventors as a challenged patent are excluded as prior art. Objective, contemporaneous proof of each inventor's contributions is essential to protect patent validity, particularly for inventions arising from joint research.

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