ABL Bio Bispecific Antibody Shows Tumor Suppression in Bile Duct Cancer... Fails to Improve Survival Markers

Phase 2/3 Results of Tovetsemig Licensed to Compass
Progression-Free Survival Doubled; Overall Survival Endpoint Not Met
Company: "Crossover to Experimental Drug in Half of Control Group Distorted Survival Metrics"

ABL Bio’s bile duct cancer treatment, Tovetumab, which was licensed out to Compass Therapeutics (hereafter "Compass") in the United States, has demonstrated efficacy in slowing tumor progression in clinical trials. However, it did not achieve improvement in overall survival.

Image of ABL Bio Headquarters. ABL Bio

On April 27, Compass announced the results of Phase 2/3 clinical trials for Tovetumab, a bispecific antibody therapy targeting patients with bile duct cancer. This was an integrated clinical trial conducted with the intention of submitting a marketing authorization application.

The clinical trial compared two groups: a control group receiving only standard chemotherapy, and a test group receiving Tovetumab in combination with standard therapy.

Analysis showed that the progression-free survival (PFS), or the period during which the disease does not worsen, in the test group was 4.7 months—almost double that of the standard treatment group, which was 2.6 months. The risk of disease progression was reduced by 56%. The objective response rate (ORR), indicating the proportion of patients whose tumors shrank, was also higher in the test group at 17.1%, compared to 5.3% in the control group.

In contrast, overall survival (OS) did not demonstrate statistical significance. The company explained that this was because 54% of patients in the control group were allowed to switch to the experimental drug during the trial (crossover), causing both groups to partially share the effects of the investigational drug. As a result, a direct comparison of survival between the drug and non-drug groups became difficult.

Tovetumab is the development name for ABL001, a bile duct cancer treatment candidate discovered by ABL Bio. It is a bispecific antibody that targets two molecules simultaneously. By concurrently blocking DLL4 and VEGF-A—angiogenesis signals involved in cancer growth—it is designed to overcome the limitations of conventional VEGF inhibitors. Global clinical development is being led by Compass.

The clinical results of Tovetumab are considered meaningful progress in the second-line treatment of bile duct cancer, where therapeutic options are limited, as it demonstrated delayed tumor progression. However, some have responded that the results fell short of expectations, as they did not translate into improved survival indicators.

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