Celltrion's Global Biotechnology Research Center. [Provided by Celltrion]
Celltrion's Global Biotechnology Research Center. [Provided by Celltrion]

Celltrion said Monday it has filed for domestic product approval of CT-P51, a biosimilar of Keytruda (pembrolizumab), the world's best-selling immunotherapy, with the Ministry of Food and Drug Safety.

The filing covers Keytruda's major indications, including non-small cell lung cancer, melanoma, gastric cancer and head and neck cancer. Celltrion demonstrated pharmacokinetic equivalence between CT-P51 and Keytruda through clinical data analysis involving 228 melanoma patients who had undergone complete resection, and confirmed comparable results in safety and immunogenicity.

Keytruda is a mega-blockbuster drug that posted global sales of about $31.7 billion (about 44 trillion won) in 2025. Celltrion plans to use the domestic filing as a starting point, then submit for approval sequentially with major global regulators — including those in the United States, Europe and Canada — to enter the first group of biosimilar approvals worldwide.

With CT-P51, Celltrion rounds out its oncology portfolio, adding an immunotherapy to its existing lineup of targeted anticancer drugs: Herzuma (breast and gastric cancer), Truxima (blood cancer) and Vegzelma (metastatic colorectal cancer, among others). The company also expects prescription synergies between CT-P51 and Vegzelma, which is used in combination with Keytruda in indications such as ovarian and cervical cancer.

The filing marks Celltrion's full-scale push into the roughly 44 trillion won ($31.6 billion) immunotherapy market. The company aims to lift the profitability and market reach of its oncology business by combining CT-P51 with its existing targeted-therapy lineup and global direct-sales network.

"We will proceed with the approval process in major global markets, starting with South Korea, without disruption in our bid to capture the global Keytruda market," a Celltrion official said. "We will maximize synergies with our existing products and next-generation pipeline, backed by stable in-house production capabilities and a solid global direct-sales network."


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