Assignor estoppel doesn’t enjoy the glamour of subject matter eligibility in the U.S. patent system, but a case heard recently at the Court of Appeals for the Federal Circuit has resurrected this relatively arcane bit of patent doctrine. The outcome of the case of Hologic v. Minerva addressed the less-than-princely sum of roughly $5 million, but Judge Kara Stoll of the Federal Circuit said this issue calls for a deeper examination by a 12-judge panel.