Arvinas, Inc. (Nasdaq: ARVN) and Pfizer Inc. (NYSE: PFE) announced preliminary data from the ongoing Phase 1b portion of the TACTIVE-U sub-study of vepdegestrant in combination with abemaciclib among patients with locally advanced or metastatic estrogen receptor positive (ER+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer. These data will be presented in a poster at the 2024 San Antonio Breast Cancer Symposium (SABCS) in San Antonio, Texas.

Preliminary results from 16 patients in the Phase 1b sub-study demonstrated a tolerable safety profile for the combination of abemaciclib 150 mg twice daily (BID) with the recommended Phase 3 monotherapy dose of vepdegestrant (200mg once daily; QD). An encouraging clinical benefit rate of 62.5% was observed among patients with both mutant ESR1 and wild-type ESR1 disease who had all been previously treated with a CDK4/6 inhibitor. 

Pharmacokinetic data demonstrated no significant drug-drug interaction between vepdegestrant and abemaciclib and no clinically meaningful effect on abemaciclib exposure was observed. In addition to tolerability, the results demonstrated a safety profile consistent with both the known properties of abemaciclib and observed data in other clinical trials for vepdegestrant. These findings support the ongoing Phase 2 portion of the study, which is evaluating full dose abemaciclib (150mg BID) in combination with vepdegestrant (200 mg QD) in post-CDK4/6 advanced breast cancer.

“The preliminary results from this Phase 1b sub-study in patients whose cancer had previously progressed after receiving a CDK4/6 inhibitor are encouraging,” said Noah Berkowitz, M.D., Ph.D., Chief Medical Officer at Arvinas. “These data further reinforce our belief that vepdegestrant can be used in multiple combination regimens across the metastatic breast cancer setting and has the potential to become a best-in-class backbone ER therapy. We are pleased to continue in the Phase 2 portion of the study evaluating the standard starting dose of abemaciclib in combination with vepdegestrant.”

“With vepdegestrant, we aim to develop a novel agent that has the potential to become a new backbone endocrine therapy in ER+ metastatic breast cancer,” said Roger Dansey, M.D., Chief Development Officer, Oncology, Pfizer. “We are pleased to see these initial results, which complement previously reported data demonstrating the potential of combination therapy with vepdegestrant to address unmet needs for patients.”