This case is an appeal by Regeneron Pharmaceuticals against a district court's denial of a preliminary injunction. Regeneron sought to prevent Amgen from marketing a biosimilar of its drug EYLEA®, arguing patent infringement. The central issue is whether Regeneron's patent requires the "VEGF antagonist" and a "buffer" in its formulation to be separate components. The Federal Circuit Court of Appeals affirmed the lower court's decision, agreeing that the patent claims imply these are distinct elements. This finding means Amgen's biosimilar, which uses the aflibercept itself for buffering, likely does not infringe Regeneron's patent. The court's analysis heavily relied on the specific language of Regeneron's patent claims and its written description.