Novartis Halts Phase III Trials of Abelacimab in Cancer-Associated Thrombosis Due to Inferior Efficacy vs. Eliquis
Johnson & Johnson
Medical Device R&D and Manufacturer
Novartis announced the discontinuation of the development of its anticoagulant antibody drug abelacimab for cancer-associated thrombosis (CAT). The Phase 3 clinical trial, which began in 2022 and recruited 1,150 patients, was terminated early after a data review showed that the drug failed to outperform Bristol-Myers Squibb (BMS) and Pfizer's blockbuster anticoagulant Eliquis. As a result, Novartis also halted another Phase 3 trial comparing the efficacy of abelacimab with Pfizer's Fragmin in patients with gastrointestinal or genitourinary cancer-related venous thromboembolism.
Despite this major setback in 2026, Novartis has not completely abandoned the development of the drug. Abelacimab is still undergoing Phase 3 clinical trials for its primary indication—atrial fibrillation (AFib), with the company planning to submit a marketing approval application for this indication in 2028. This AFib trial has recruited 1,900 patients who are unsuitable for oral anticoagulants like Eliquis and Xarelto and is comparing the drug against a placebo.
Reviewing the development history of this drug, Novartis co-invested $250 million with Blackstone in 2019 to spin off and establish Anthos Therapeutics, which was dedicated to developing this Factor XI/XIa inhibitor aimed at preventing thrombosis without increasing the risk of bleeding. In Phase 2 trials, abelacimab demonstrated superior efficacy by reducing venous thromboembolism by 80% compared to enoxaparin, with a lower bleeding rate than the older anticoagulant Xarelto. This prompted Novartis to repurchase Anthos in February 2025 for a $925 million upfront payment (and up to $2.15 billion in potential milestone payments), reclaiming control of the three Phase 3 trials expected to be completed in 2026.
Novartis' tortuous experience reflects the fierce competition and huge development risks in the entire Factor XI inhibitor track, as major pharmaceutical companies are all trying to gain a share in this market, which is about to face competition from non-vitamin K oral anticoagulant generics.
Just a few months ago, on November 14, 2025, Bristol-Myers Squibb (BMS) and Johnson & Johnson (J&J) also terminated their trial of the Factor XIa inhibitor milvexian for Acute Coronary Syndrome (ACS) early due to insufficient efficacy. The Independent Data Monitoring Committee determined that the trial could not achieve its primary efficacy endpoint on top of standard antiplatelet therapy, causing BMS shares to drop by 6% in pre-market trading.
The trial, which was originally planned to recruit 16,000 patients and conclude by the end of 2026, has failed, delivering a heavy blow to ACS patients. If successful, milvexian could have become the first drug of its kind approved for ACS. However, due to the lack of new safety issues in the interim analysis, BMS and Johnson & Johnson are continuing to advance milvexian trials for atrial fibrillation and secondary stroke prevention (SSP).
On the same track, Bayer's Factor XIa inhibitor asundexian was prematurely terminated in 2023 for atrial fibrillation trials due to a rate of fatal cardiovascular events in patients that was twice as high as that of Eliquis. However, Bayer subsequently demonstrated in another trial that asundexian significantly reduced the risk of stroke, paving the way for the German pharmaceutical company to file for approval in 2026.
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