Samsung Bioepis leads, Celltrion gives chase in race for Keytruda biosimilar market

With the patent expiry of Keytruda (pembrolizumab) — the world's top-selling drug — drawing closer, South Korea's two leading biotech companies, Samsung Bioepis and Celltrion, have entered a head-to-head contest for the global immuno-oncology biosimilar market, valued at 44 trillion won ($31.9 billion). Samsung Bioepis has surged ahead by completing a large-scale global Phase 3 trial and filing preemptive regulatory approvals, while Celltrion has now joined the race in earnest by submitting a domestic approval application.

Celltrion filed for domestic product approval of its Keytruda biosimilar CT-P51 with the Ministry of Food and Drug Safety on Tuesday. The company demonstrated pharmacokinetic equivalence with the original Keytruda in a trial involving 228 melanoma patients who had undergone complete resection, and confirmed comparable results in safety and immunogenicity. Celltrion plans to follow the domestic filing with sequential submissions to major global regulators, including the US Food and Drug Administration and the European Medicines Agency, as it moves to close the gap with the front-runners.

Samsung Bioepis has been the clear pacesetter in the global development race. The company completed its global Phase 3 trial of Keytruda biosimilar SB27 ahead of rivals and filed preemptive approval applications with key regulators. Notably, it ran a large-scale, multinational Phase 3 trial in more than 600 non-small cell lung cancer patients — the indication that accounts for the bulk of Keytruda's total sales — securing efficacy and safety data that position it to win the confidence of prescribers worldwide.

Keytruda, developed by US drugmaker Merck, recorded annual global sales of approximately $31.7 billion last year, cementing its status as the world's best-selling drug and the dominant immuno-oncology blockbuster. Given the unprecedented scale of the market for a single drug, whichever biosimilar reaches the market first when the original compound's patent expires stands to capture the early prescription market and lock in market share. For South Korean companies eyeing leadership in the global biosimilar space, Keytruda represents the single most consequential battleground for future earnings.

The two companies' commercialization paths and market strategies stand in sharp contrast. Samsung Bioepis, holding the lead, is pursuing a strategy of rapid early market-share capture by leveraging the established local marketing networks and distribution infrastructure of multiple proven global partners — including Organon, Biogen and Sandoz. Drawing on its track record of successfully launching numerous blockbuster biosimilars in major global markets, the company aims to lock up key hospital and private-insurer prescription channels across the United States and Europe.

Celltrion, coming from behind, is betting on cost competitiveness backed by large-scale in-house production facilities, combined with fully direct-sales distribution networks already operating in the US and major European markets. The company is particularly targeting strong synergies through bundled prescriptions pairing Keytruda with its own targeted anticancer drug Vegzelma — used alongside Keytruda in ovarian and cervical cancers — and through pharmacy benefit manager listing negotiations in the US. It is also actively pursuing linkages with its next-generation drug pipeline, including antibody-drug conjugates currently in development.

Global biosimilar heavyweights including Sandoz, Amgen and Coherus have also entered the Keytruda development race, and competition for first-mover status — along with patent disputes and early-launch rivalries — is expected to intensify further. South Korean biotech companies are simultaneously pursuing detailed legal and regulatory strategies to achieve early market entry timed to patent expiries in each country, countering the originator's patent defense tactics.

The Keytruda biosimilar contest between South Korea's two biotech giants marks a pivotal expansion of the K-biosimilar arena — previously centered on autoimmune diseases (TNF-alpha inhibitors) and targeted therapies — into the mega-scale immuno-oncology market.

As South Korea's leading biotech companies bring distinct clinical development strategies and global commercialization capabilities to bear on the world's largest drug market, attention is now focused on whether Korean firms can seize the lead in the next generation of blockbuster biosimilars.