On Appeal from the United States District Court for the Northern District of New York Plaintiff-Appellant Regeneron Pharmaceuticals, Inc. appeals from a judgment of the United States District Court for the Northern District of New York (Hurd, J.) dismissing under Fed. R. Civ. P. 12(b)(6) Regeneron’s claims alleging antitrust violations and tortious interference with contract. On appeal, Regeneron contends that the district court erred in concluding that it failed to plead the existence of a relevant antitrust market and also erred in dismissing, as untimely, its tortious interference claim. Because we agree with Regeneron on both grounds, we REVERSE the judgment of the district court and REMAND for further proceedings consistent with this opinion. BARRINGTON PARKER, C.J. 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-VEGF treatments and concluded that, because of those similarities, both versions compete in the same relevant market. The court further concluded that Regeneron could not state a Sherman Act claim under Walker Process because a proposed relevant market cannot be coextensive with the bounds of a patent. Additionally, the district court dismissed Regeneron’s tortious interference claim as untimely, holding that Regeneron’s pleadings failed to establish that Novartis should be equitably estopped from invoking the statute of limitations. On appeal, Regeneron argues that the district court improperly dismissed its antitrust claims both because it plausibly alleged that anti-VEGF PFSs constitute their own product market — distinct from the market for vials — and because the district court applied an improper standard to its claims under Walker Process. Regeneron also argues that the district court improperly rejected its equitable estoppel argument because Novartis and Vetter took steps to prevent Regeneron from learning of Novartis’s tortious interference until after the limitations period had expired. We agree with Regeneron. We therefore REVERSE the judgment of the district court and REMAND for further proceedings consistent with this opinion. BACKGROUND1 I. Factual Background Regeneron and Novartis are biotechnology and pharmaceutical companies that produce drugs that treat the overproduction of VEGF. Vetter, a supplier of drug “filling” services, has contracted with both Regeneron and Novartis to fill vials and PFSs with their anti-VEGF treatments. The overproduction of VEGF, if left untreated, can cause patients to “see the world as if through distorted lenses: straight lines may appear bent, central vision may be reduced, colors may be dulled, and patients may see haziness.” J. App’x at 349 (Am. Cmplt. 38). Patients may also “experience a well-defined blurry or blind spot in their central field of vision,” or even suffer permanent blindness. Id. (Am. Cmplt.
38-39). EYLEA and LUCENTIS, produced by Regeneron and Novartis, respectively, are the primary anti-VEGF drugs approved by the FDA. Vetter has historically provided drug filling services to both Regeneron and Novartis, filling vials and PFSs with the anti-VEGF medicines they produce. While anti-VEGF vials and PFSs contain the same active ingredients and are used to combat the same condition, their differing formats have significant implications for how physicians treat patients. When delivered in vials, the treatments come “with multiple components, including the vialed biologic, two separate needles, and a plastic syringe.” J. App’x at 360 (Am. Complt. 76). Doctors using the vials must, under sterile conditions, “use the filter needle to withdraw the correct amount of the anti-VEGF from the vial and then switch to an injection needle before injecting the properly measured dosage into the patient’s eye.” Id. This process is cumbersome and, if handled incorrectly, introduces a heightened risk of endophthalmitis — a harmful inflammation of the interior of the eye. PFSs, on the other hand, are easier to administer and, according to the parties, “permit more safe, effective and efficient injections of VEGF-antagonists into the eye.” J. App’x at 362 (Am. Cmplt. 82) (quoting Novartis’s patent infringement complaint). PFSs enable physicians to administer the required dose more precisely and with a lower risk of foreign particles entering the eye, thereby increasing dose accuracy and clinical efficiency. See id. at 361-62 (Am. Cmplt.
