In this en banc reconsideration of Marine Polymer Technologies, Inc. v. Hemcon, Inc., a key issue reviewed by the US Court of Appeals for the Federal Circuit was whether, in an ex parte patent reexamination, intervening rights can apply to claims that have not been amended or are not new, even though the patent owner made narrowing arguments during the reexamination.

In 2006, Marine Polymer sued HemCon for infringement of US Patent 6,864,245 ('245 patent), a patent for preparations of a polymer that helps stops bleeding. The US District Court for the District of New Hampshire found that HemCon infringed the '245 patent, and it awarded Marine Polymer damages and issued a permanent injunction against HemCon.

However, while the district court case was pending, HemCon filed an ex parte reexamination of the '245 patent with the USPTO, where the main issue was construction of the word "biocompatible" as used in the '245 patent. During the reexamination, Marine Polymer overcame examiner objections by arguing for narrower construction of "biocompatible" as adopted by the district court and cancelling certain dependent claims that conflicted with the district court's narrower construction. The USPTO ultimately confirmed the claims in dispute to be patentable as originally issued after the district court had entered final judgment. HemCon appealed the district court judgment to the Federal Circuit.

On September 26, 2011, a three judge panel of the Federal Circuit reversed the district court's infringement judgment and vacated the permanent injunction and damages awards, finding that HemCon had acquired absolute intervening rights during the ex parte reexamination of the '245 patent. The panel agreed with HemCon that arguments made by Marine Polymer during the reexamination that narrowed the scope of the asserted claims triggered intervening rights, even though the actual language of the claims was not changed.

On January 20, 2012, the Federal Circuit granted Marine Polymer's petition for an en banc rehearing and vacated the panel decision.

On reconsideration en banc, an equally-divided court affirmed the district court's judgment concerning claim construction, infringement and damages.

A 6-4 majority of the full court then concluded as an alternative ground that HemCon did not acquire intervening rights as a result of the ex parte reexamination of the '245 patent.

According to the majority, the plain language of Section 307(b) of the Patent Act (which governs intervening rights in ex parte reexaminations), limits intervening rights to only those claims that are "amended or new" following the reexamination. If the asserted claim is not amended or new after reexamination, no further inquiry is needed. If the claim is amended or new, then the next step is to assess the substantive effect of any changes under 35 U.S.C. § 252 (concerning intervening rights arising out of reissued patents, which is incorporated by reference into Section 307(b)).

In this case, Marine Polymer made arguments during the reexamination that potentially changed the scope or interpretation of the relevant claims. However, intervening rights did not apply as a matter of law because the actual language of the claims was not changed and no new claims were added.

The Federal Circuit's en banc decision is favorable for many patent owners concerned that the earlier panel opinion's expanded view of intervening rights would have limited their ability to make substantive arguments during reexamination to defend the validity of their patents without triggering intervening rights.

However, as HemCon and the dissent noted, the decision could encourage patent holders to attempt to rely on arguments rather than claim amendments to effectively change, and thereby preserve, otherwise invalid claims during reexamination without triggering intervening rights against those claims.