Celltrion Halts EU Keytruda Biosimilar Trial and Trims FDA Study to 220 Patients as Global Regulators Ease Phase 3 Rules
TL;DR - Celltrion terminated its EU Phase 3 trial for CT-P51 (pembrolizumab biosimilar to Keytruda) on July 14, citing evolving EMA guidance - FDA Phase 3 enrollment cut from 606 to 220 patients via July 6 amendment — a roughly 64% reduction - FDA and EMA are both moving toward waiving or drastically simplifying Phase 3 clinical requirements for biosimilars - South Korea's MFDS issued revised biosimilar approval guidelines effective July 14, allowing approval without large-scale Phase 3 data for certain products - Samsung Bioepis (SB27) had already announced positive Phase 3 pembrolizumab biosimilar data, putting competitive pressure on Celltrion
Part A — What Was Disclosed
Celltrion (068270.KS) said on July 14 that it has notified the European Medicines Agency of the early termination of its EU Phase 3 clinical trial for CT-P51, a biosimilar of MSD's Keytruda (pembrolizumab), and has voluntarily withdrawn the EU investigational new drug application (IND).
The affected trial compared CT-P51 against originator Keytruda in patients with previously untreated metastatic non-squamous non-small cell lung cancer (NSCLC). The company said European Union member states were excluded from the global trial's participating country list, eliminating the need to maintain a separate EU IND.
The global Phase 3 trial in non-EU countries continues, the company confirmed.
One week earlier, on July 6, Celltrion filed an amendment with the U.S. Food and Drug Administration to reduce the number of Phase 3 trial participants from approximately 606 to around 220. The FDA had originally approved the trial design in August 2024, setting a two-year comparison window.
The strategic pivot reflects a broader regulatory shift. The FDA recently released a draft guidance allowing biosimilar developers to skip Phase 3 clinical trials if sufficient analytical and earlier-phase data demonstrate biosimilarity. The EMA has signaled a parallel direction, indicating that quality-based comparability alone may be sufficient to obtain marketing authorisation for certain biosimilars. South Korea's Ministry of Food and Drug Safety (MFDS) issued a revised biosimilar approval regulation on July 14, effective immediately, enabling products meeting specified criteria to obtain approval without large-scale Phase 3 trial data.
In a separate announcement on the same day, Celltrion disclosed that it received a renewal of the triple-A (AAA) rating from Korea Customs Service's Authorized Economic Operator (AEO) programme — the highest certification for export-import safety compliance. Celltrion is the only pharmaceutical or biopharmaceutical company among Korea's 773 AEO-certified firms to hold the AAA designation, which waives 100% of customs document requirements and physical inspections through 2030.
Part B — What It Means for KOSPI Investors
The Race for the World's Best-Selling Drug's Biosimilar
Pembrolizumab is MSD's flagship immune checkpoint inhibitor — one of the world's top-grossing drugs, generating annual revenues in excess of USD 25 billion. Patent expiry in key markets is expected to begin around 2028–2031, opening a biosimilar window that could rival any in biopharmaceutical history. South Korean firms are among the most aggressive global competitors for this prize.
Celltrion's decision to streamline rather than abandon its programme should be read as acceleration, not retreat. A trial reduction from 606 to 220 patients is not a setback — it is a calculated response to regulators effectively de-risking the path to approval. Fewer participants means faster enrolment, a shorter trial timeline, and materially lower out-of-pocket development costs at a moment when Celltrion is simultaneously advancing CT-P44 (a biosimilar to Darzalex/daratumumab), CT-P52 (Taltz/ixekizumab), and CT-P55 (Cosentyx/secukinumab).
The EU IND withdrawal is the more nuanced move. Celltrion is not exiting the European market — it is restructuring its trial geography so that non-EU data alone will carry the global submission. Under current EMA standards, sponsors can rely on multinational trial data even without EU-specific sites, provided the patient population is representative. The decision reduces regulatory and logistical overhead without sacrificing the EU filing pathway.
Samsung Bioepis Is Ahead — but the Gap Is Smaller Than It Looks
Samsung Bioepis (a joint venture 50.1% owned by Samsung BioLogics and 49.9% by Biogen) made headlines when it released positive Phase 3 data for SB27, its own pembrolizumab biosimilar, positioning itself as the "first developer to announce global Phase 3 results" in this category. That lead matters: a first-to-file advantage in the US could translate to 12 months of reference-product exclusivity under the Biologics Price Competition and Innovation Act.
However, Celltrion's streamlining narrows the gap. If Celltrion's amended 220-patient trial enrols faster than Samsung Bioepis's larger study and both reach submission around the same window, the competitive dynamic shifts. The pembrolizumab biosimilar market will also be large enough — potentially USD 5–8 billion by 2030 on conservative penetration assumptions — that multiple players can coexist.
Additional competitors include Formycon (partnered with Zydus), which has expressed confidence in filing the first US Biologics License Application in this category, and several Chinese manufacturers targeting lower-margin markets.
Valuation Context
Celltrion shares have performed strongly in 2026 on the back of record Q2 2026 earnings — operating profit of KRW 430 billion (+77.3% YoY), according to the company's July preliminary disclosure. The CT-P51 news is unlikely to move the stock sharply in either direction on its own, but it matters for the medium-term pipeline narrative. If the FDA's simplified pathway becomes final and Celltrion can reach market for Keytruda biosimilar in 2027–2028 instead of 2029–2030, the net present value of the programme expands materially.
The AEO AAA certification, while a minor operational item, reinforces that Celltrion's manufacturing and compliance infrastructure — critical for biosimilar market access in regulated markets — meets the highest standards.
| Metric | Detail |
|---|---|
| Drug | CT-P51 (pembrolizumab biosimilar, reference: Keytruda/MSD) |
| EU Phase 3 status | Terminated; EU IND voluntarily withdrawn (July 14, 2026) |
| FDA Phase 3 patients | 606 → 220 (–64%; amended July 6, 2026) |
| Global trial (non-EU) | Continuing |
| Original FDA approval | August 2024 |
| Indication | Metastatic non-squamous NSCLC (1L) |
| Key regulator signals | FDA draft guidance (Phase 3 waiver pathway); EMA (quality-only approval pathway); Korea MFDS revised rules (July 14, 2026) |
| Main competitor | Samsung Bioepis SB27 (Phase 3 data released); Formycon/Zydus |
| Reference drug global revenue | USD ~25 billion/year (MSD Keytruda) |
Risks
The FDA draft guidance on Phase 3 waivers remains in draft form. If the final rule is more restrictive than the proposal, Celltrion may need to revert to a larger trial. Pembrolizumab's mechanism — an immune checkpoint inhibitor — also carries higher regulatory scrutiny for biosimilarity demonstration than monoclonal antibodies for autoimmune conditions, meaning the simplified pathway may face higher evidentiary thresholds.
Celltrion (068270.KS) is listed on the Korea Stock Exchange. Samsung Bioepis is not publicly listed independently; its parent Samsung BioLogics (207940.KS) is KOSPI-listed. This article is not investment advice.
Sources: - Chosun Biz — 셀트리온, CT-P51 유럽 3상 조기 종료 (July 14, 2026) - etnews — 셀트리온, AEO AAA 갱신 (July 14, 2026) - Pearce IP — Celltrion Streamlines Ph 3 Global Trial for Biosimilar to Keytruda (July 6, 2026) - Korea Biomed — Celltrion wins EMA approval to cut CT-P55 Phase 3 trial size
