What is Assignor Estoppel in Patent Law?
Assignor Estoppel Limitations
In Minerva Surgical, Inc. v. Hologic, Inc., the Supreme Court reaffirmed the continued viability of assignor estoppel in patent law while clarifying that the doctrine applies only when an inventor’s later invalidity challenge directly contradicts warranties made at the time of assignment. The decision narrows the doctrine by defining clear limits on when estoppel applies.
Blanket Assignments May Not Trigger Assignor Estoppel — Assignor estoppel does not apply when an inventor assigns future inventions before any specific patent exists. In these situations, such as employment-related blanket assignments, the inventor has not warranted the validity of any particular patent, eliminating the contradiction that estoppel is meant to prevent.
Changes in Patent Law Can Eliminate Estoppel — If later legal developments render a previously valid patent invalid, assignor estoppel does not bar the inventor from challenging validity. Because the law and not the inventor’s prior representations creates the inconsistency, there is no unfair contradiction to estop.
Post-Assignment Claim Expansion Can Defeat Estoppel — When patent claims are materially broadened after assignment, such as through continuation applications, the inventor may challenge those claims. The Court held that an inventor cannot be estopped from disputing claims that extend beyond the scope of what was originally assigned.
For more information, see our blog post Assignor Estoppel in Patent Law: Important Limitations Defined.
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