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Fengqian Chen: Another Reality Check for the Factor XI Inhibitor Race – Novartis’ Abelacimab Setback
Fengqian Chen/LinkedIn
Apr 29, 2026, 02:52

Fengqian Chen: Another Reality Check for the Factor XI Inhibitor Race – Novartis’ Abelacimab Setback

Fengqian Chen, Regional Director at Biocytogen, shared a post on LinkedIn:

“Novartis’ Abelacimab Setback: Another Reality Check for the Factor XI Inhibitor Race

Novartis has halted development of abelacimab in cancer-associated thrombosis after a Phase 3 study failed to outperform Eliquis.

This is not a small signal.

The trial began in 2022, enrolled 1,150 patients, and was terminated early after data review.

Novartis also stopped a second Phase 3 study comparing abelacimab with Fragmin in patients with venous thromboembolism associated with gastrointestinal or genitourinary cancers.

Novartis and Blackstone Life Sciences invested $250 million in 2019 to launch Anthos Therapeutics as a spinout focused on developing abelacimab.

The original promise of abelacimab was compelling:

  • Prevent thrombosis by inhibiting factor XI/XIa, while reducing the bleeding risk that has long limited traditional anticoagulants.

That thesis was supported by earlier Phase 2 data showing strong reductions in venous thromboembolism and a favorable bleeding profile.

But Phase 3 development is where biological elegance meets clinical reality.

And right now, the factor XI/XIa inhibitor field is proving difficult.

Bristol Myers Squibb and Johnson and Johnson recently stopped their Phase 3 ACS trial of milvexian after an independent monitoring committee concluded it was unlikely to meet the primary efficacy endpoint.

Bayer’s asundexian also suffered a major setback in atrial fibrillation after an early trial termination, though the company later found a more promising path in stroke-risk reduction.

The message is becoming clearer:

  • Factor XI inhibition remains one of the most attractive ideas in anticoagulation — but it is not a guaranteed upgrade over today’s standard of care.

The field must now answer several hard questions:

  • Which indications truly benefit from factor XI/XIa inhibition?
  • Can these drugs show superiority, not just theoretical safety advantages?
  • Will reduced bleeding risk be enough if efficacy falls short?
  • Can developers find the right patient populations before the commercial window narrows?

Importantly, Novartis has not abandoned abelacimab entirely.

The drug remains in Phase 3 development for atrial fibrillation in patients unsuitable for oral anticoagulants, with a planned regulatory submission in 2028.

That may now be the most important test for the program.

The factor XI story is far from over.

But the bar has moved higher.

In anticoagulation, better safety is not enough.

The next generation must prove it can deliver clinically meaningful protection where existing therapies already set a very high standard.

Look up references below.

Study Title: A Study Comparing Abelacimab to Dalteparin in the Treatment of Gastrointestinal/​Genitourinary Cancer and Associated VTE (MAGNOLIA)

Study Title: A Study Comparing Abelacimab to Apixaban in the Treatment of Cancer-associated VTE (ASTER)”

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Anthos Therapeutics Blackstone Life Bristol Myers Squibb Fengqian Chen Health Hematology Hemostasis Hemostasis News Hemostasis Today Johnson and Johnson Medicine Novartis
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