As competition rises in the Keytruda (pembrolizumab) biosimilar space, Celltrion Inc. is the latest to announce that it filed an IND application to the U.S. FDA to start a global phase III trial for its own Keytruda biosimilar, dubbed CT-P51. Incheon, South Korea-based Celltrion, which previously said it would differentiate from the pack by developing an easier-to-administer subcutaneous biosimilar of pembrolizumab, announced June 17 plans to start a global comparative phase III study of CT-P51 and Keytruda.