The resolution of this appeal turns on the definition of the relevant antitrust product market. The products in question are prescription medications used to treat the overproduction of vascular endothelial growth factor (“VEGF”), a naturally occurring protein that, if overproduced, can lead to various eye disorders and, in some cases, to permanent blindness. Both Plaintiff-Appellant Regeneron Pharmaceuticals, Inc. (“Regeneron”) and Defendant-Appellees Novartis Pharma AG, Novartis Technology LLC, and Novartis Pharmaceuticals Corporation (collectively, “Novartis”) produce “anti-VEGF” medications to combat the overproduction of VEGF. Regeneron produces EYLEA, while Novartis produces LUCENTIS.

For several years after they were first introduced, anti-VEGF medications were packaged into vials and administered in a two-step process. A doctor would first fill a syringe with medicine from an anti-VEGF vial and then inject the drug into a patient’s eye. The newer versions of the medications are sold in prefilled syringes (“PFSs”) and administered in one step. PFSs contain the same medication as vials but are injected directly into the patient’s eye. This simpler process carries a significantly lower risk of complications and infections and is now the preferred way of administering anti-VEGF medications. The pivotal issue in this appeal is whether anti-VEGF medications in vials and PFSs compete in the same or in different product markets.

Starting around 2005, Regeneron recognized the comparative advantages of PFSs over vials and, for approximately the next fifteen years, sought to develop and obtain FDA approval for an anti-VEGF PFS treatment. At the beginning of this development process, Regeneron contracted with Defendant-Appellee Vetter Pharma International GmbH (“Vetter”) to collaborate on a PFS version of its EYLEA drug. At that time, Vetter was already providing non-exclusive “filling” services for Regeneron’s vial version of EYLEA. Unbeknownst to Regeneron, however, Vetter allegedly entered into a similar agreement with Novartis in 2009 to produce a competing PFS version of Novartis’s drug, LUCENTIS.

Regeneron alleges that from 2009 to 2015, Novartis and Vetter fraudulently concealed Vetter’s contributions to a patent that Novartis obtained in 2015 for a PFS version of LUCENTIS. Then, after unlawfully obtaining the patent, Novartis and Vetter allegedly took steps to keep Regeneron out of the anti-VEGF PFS market until 2019, when Regeneron finally released its own PFS version of EYLEA.

Regeneron argues that these steps delayed the release of its anti-VEGF PFS by several years and enabled Novartis to increase its market share during this period.

In July 2020, Regeneron sued Novartis and Vetter in the United States District Court for the Southern District of New York, which transferred the case to the Northern District. The Amended Complaint asserts five claims: two claims against Novartis of attempted monopolization under Walker Process Equip., Inc. v.

Food Mach. & Chem. Corp., 382 U.S. 172 (1965), in violation of Section 2 of the Sherman Act, 15 U.S.C. § 2 ; one claim against Novartis of non-Walker Process attempted monopolization in violation of Section 2; one claim against Novartis and Vetter of unreasonable restraint of trade in violation of Section 1 of the Sherman Act, 15 U.S.C. § 1 ; and one claim against Novartis of tortious interference with contract in violation of New York law.

Novartis and Vetter moved under Fed. R. Civ. P. 12(b)(6) to dismiss the Amended Complaint, and the district court (Hurd, J.) granted the motion. As to the antitrust claims, the court reasoned that Regeneron failed to allege plausibly that the relevant antitrust market is properly limited to anti-VEGF PFSs, to the exclusion of vials. The district court focused on the functional similarities between the PFS and vial versions of Regeneron’s and Novartis’s respective anti-