Celltrion and Samsung Bioepis intensify Korean biosimilar race for Keytruda

As global sales of blockbuster cancer drug Keytruda surpassed 43 trillion won ($31.5 billion) last year and its patent expiration approaches, biopharmaceutical companies around the world are accelerating the development of biosimilars referencing Keytruda.

Keytruda (ingredient: pembrolizumab), developed by U.S. pharmaceutical company Merck, known as MSD outside North America, is a third-generation immune checkpoint inhibitor used to treat a wide range of cancers, including non-small cell lung cancer (NSCLC), melanoma, and head and neck cancers.

The drug blocks the PD-1 protein on T cells, preventing interaction with PD-L1 expressed by tumor cells and thereby reactivating immune responses to attack cancer cells. It currently holds more than 30 approved indications globally.

Among Korean contenders, Celltrion gave the most recent update, stressing that it has received approval from the Ministry of Food and Drug Safety to initiate a phase 3 clinical trial of its Keytruda biosimilar candidate CT-P51 on Monday. The trial will enroll 606 patients with metastatic non-squamous NSCLC who have not received prior systemic therapy.

The study is designed to compare the efficacy and safety of CT-P51 and Keytruda over a two-year period, using a randomized, double-blind, active-controlled, parallel-group design.

Celltrion said the trial aims to demonstrate biosimilarity in terms of therapeutic effect and safety profile, with plans to expand indications in line with those of the original drug.

“We aim to obtain approval for CT-P51 not only in metastatic NSCLC, but also across all other indications approved for Keytruda, enabling us to broaden our market reach and increase revenue,” the company said.

The Korean trial follows the company's earlier receipt of investigational new drug (IND) approval from the U.S. FDA for a global phase 3 study of CT-P51 in August 2024.

Meanwhile, another biosimilar powerhouse, Samsung Bioepis, has also been racing to develop a biosimilar version of Keytruda.

The company launched a global “overlapping” clinical strategy for its own Keytruda biosimilar, SB-27. Last year, the company began conducting phase 1 and phase 3 trials concurrently—an approach permitted in biosimilar development to reduce time-to-market.

The company launched a phase 1 trial of SB-27 in January 2024 across four countries, including Korea,  enrolling patients with NSCLC, and later launched a phase 3 global comparative trial in April 2024 involving 616 patients in 14 countries.

While new drug development typically follows a sequential process from phase 1 to phase 3, biosimilars benefit from regulatory pathways that allow simultaneous or expedited trial designs. This has positioned both Celltrion and Samsung Bioepis to potentially become early entrants in the high-value immunotherapy biosimilar market.