Formycon First to Enter FDA Review in $42 Billion Keytruda Biosimilar Race

Keytruda, Merck’s blockbuster cancer immunotherapy drug, generated approximately $31.7 billion in sales in 2025. The global race to capture a share of the market for biosimilars of Keytruda, the world’s top-selling drug by revenue, has reached a key regulatory milestone in the United States. Germany’s Formycon has become the first company to publicly announce that the U.S. Food and Drug Administration has accepted a Keytruda biosimilar application for review, drawing attention to the development and patent strategies of other contenders, including South Korea’s Samsung Bioepis and Celltrion. Formycon and India’s Zydus Lifesciences announced on Oct. 13 (local time) that the FDA had accepted their biologics license application for FYB206, a proposed biosimilar to Keytruda, for review. The companies said this was the first publicly announced FDA review of a Keytruda biosimilar application. Formycon expects a decision on approval in the third quarter of 2027, based on the anticipated review timeline. Formycon’s early progress reflects its streamlined clinical development strategy. After discussions with the FDA, the company opted to forgo a large-scale comparative Phase 3 efficacy trial and instead focus on analytical and functional comparability assessments and a comparative pharmacokinetic study. It ended a clinical trial involving patients with non-small cell lung cancer after 25 patients had enrolled, relying instead on evidence from its DAHLIA study, which assessed pharmacokinetic equivalence in patients with melanoma. The approach is expected to save tens of millions of euros in research and development costs and shorten the development timeline. South Korean companies Samsung Bioepis and Celltrion are pursuing different approaches. Samsung Bioepis demonstrated comparability with Keytruda in a global Phase 3 trial involving 555 patients with non-small cell lung cancer and applied for approval from South Korea’s Ministry of Food and Drug Safety in August. Celltrion also filed for domestic approval that month. The company is seeking to improve development efficiency after receiving FDA approval for a plan to reduce the size of its Phase 3 trial from the original 606 participants to 220. Keytruda, developed by U.S.-based MSD, generated approximately $31.7 billion in sales last year, equivalent to about 42.4 trillion won. At least 13 companies worldwide are developing biosimilars of the blockbuster cancer drug. Keytruda’s core U.S. composition-of-matter patent is scheduled to expire in December 2028, but patents covering manufacturing processes and methods of use extend into 2029, leaving the timing of actual market entry uncertain. Patent disputes are also intensifying ahead of potential market entry. Celltrion recently filed a lawsuit in Canada’s Federal Court seeking to invalidate two patents related to Keytruda combination therapies. Samsung Bioepis is also laying the legal groundwork for market entry, asserting that it has standing in Canada to seek declarations of patent invalidity and non-infringement while challenging arguments made by Merck. In response to the biosimilar challenge, MSD is pursuing a transition to Keytruda Qlex, a subcutaneous formulation of the drug. Unlike biosimilars targeting the intravenous formulation, Keytruda Qlex is protected by U.S. patents extending through 2043. MSD expects 30% to 40% of future demand for solid-tumor treatments to shift to the subcutaneous formulation. As a result, biosimilar developers face the challenge of not only securing regulatory approval but also competing in a market that may increasingly shift toward the newer formulation.