Since late 2019, the Patent Trial and Appeal Board (PTAB) has been steadily expanding the scope of its discretion to deny institution for inter partes review (IPR) petitions for reasons other than the merits. Perhaps the most controversial part of this expansion has been a pair of precedential decisions collectively known as the NHK-Fintiv rule, which allows the PTAB to consider the status of parallel district court litigation. Now, the Federal Circuit has weighed in on the appealability of an NHK-Fintiv denial—and has determined that appellants face an extremely “narrow” path for challenging such decisions. On March 12, the court held in Mylan Laboratories v. Janssen Pharmaceutica that mandamus relief is available for a NHK-Fintiv denial, but only to address a “colorable constitutional claim” (2021-1071).