Pfizer terminates TACTIVE-U Sub-Study C of vepdegestrant plus samuraciclib
Enrollment closed after 11 patients for strategic business reasons, not safety, with Phase 2 and drug interaction portions never started.
Pfizer has terminated Sub-Study C of the TACTIVE-U trial, a Phase 1b/2 umbrella study testing vepdegestrant (ARV-471/PF-07850327) in combination with samuraciclib in people with ER-positive, HER2-negative advanced or metastatic breast cancer. According to the trial record, last updated October 27, 2026, enrollment was permanently closed for strategic business reasons after 11 participants enrolled in Phase 1b.1 The decision was not related to safety, efficacy, benefit-risk, or participant welfare, and the planned Phase 2 and drug-drug interaction components were not initiated.1
The study began on January 10, 2024, and both primary completion and overall study completion are listed as September 10, 2026. It was first posted on ClinicalTrials.gov on November 9, 2023.
Pfizer served as lead sponsor, with Arvinas Estrogen Receptor, Inc., Carrick Therapeutics Limited, and Rigel Pharmaceuticals, Inc. listed as collaborators.
In the sub-study design, all participants received vepdegestrant and samuraciclib, both taken once daily by mouth.1 The protocol called for evaluating safety, antitumor activity, and pharmacokinetics of ARV-471 with samuraciclib as part of a backbone therapy strategy combined with other anticancer agents considered clinically relevant in ER-positive breast cancer.1
Before termination, the trial record listed 23 sites in 4 countries: United States, Belgium, France, Italy.1
Fact check notes
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Enrollment ultimately reached 11 participants, as recorded in the design section of the listing.
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