Aug 15, 2022

Claim Cancellation Before Assignment Does Not Preclude Assignor Estoppel

Before Stoll, Clevenger, and Wallach. Appeal from the United States District Court for the District of Delaware.

Summary: Despite cancelling a claim prior to assignment, assignor estoppel still applied to bar invalidity defenses against a related claim because the assignor warranted the validity of the cancelled claim and the cancelled claim was not directed to subject matter materially broader than the related claim.

Hologic, Inc. (“Hologic”) sued Minerva Surgical, Inc. (“Minerva) for patent infringement and the district court barred Minerva’s invalidity defenses under the doctrine of assignor estoppel. The Federal Circuit affirmed the decision and Minerva petitioned the Supreme Court, requesting that the Court “discard this century-old form of estoppel.” The Supreme Court held that assignor estoppel remains a valid doctrine, but that it comes with limits, and remanded the case for the Federal Circuit to determine whether the asserted claim was “materially broader” than the claims assigned to Hologic such that assigner estoppel should not apply. On remand, the Federal Circuit affirmed upon analyzing whether (1) the inventor warranted the validity of a claim from a parent application that was cancelled prior to assignment; and (2) whether the cancelled claim was materially broader than an asserted claim.

Regarding validity, Minerva argued that the inventor had not warranted validity of the cancelled claim because it was cancelled prior to assignment. The Federal Circuit rejected this argument because the claim was cancelled “without prejudice” due to a restriction requirement. Moreover, the inventor successfully overcame the Examiner’s rejection of the claim for anticipation prior to its cancellation. Given this posture, the Federal Circuit explained that the cancellation was for reasons other than patentability and was not a concession of unpatentability. Furthermore, the Federal Circuit explained that cancellation did not nullify the claim, that it remained viable for further prosecution in a divisional application, and the inventor’s assignment conveyed rights to any divisional applications not yet filed. Thus, the cancelled claim traveled with the assignment to Hologic and its validity had been warranted by its original filing, its successful defense during prosecution, and in the inventor’s assignment stating that he had “no present knowledge from which [he] could reasonably conclude” that the assigned rights were invalid or unenforceable.

As for claim breadth, Minerva argued that the cancelled claim was “materially broader” because it was limited to a “moisture-permeable” device while the asserted claim was limited to a “moisture-impermeable” device. The Federal Circuit disagreed upon analyzing the claim language (which did not contain an express limitation), the written description (which described “moisture-permeability” only as being “preferable”), and applied the doctrine of claim differentiation to hold that the cancelled claim was not limited to “moisture-permeable” devices and instead encompassed both “moisture-permeable” and “moisture-impermeable” devices. Thus, the asserted claim was not materially broader than the cancelled claim, and assignor estoppel applied.

Editor: Paul Stewart

Written by: Nefi Oliva and Andrew Morrell