Arvinas-Pfizer Partner Cancer Drug Trial Shows 63% Clinical Benefit In Breast Cancer Patients

On Tuesday, Arvinas Inc. ARVN and Pfizer Inc. PFE announced preliminary data from the ongoing Phase 1b portion of the TACTIVE-U sub-study of vepdegestrant in combination with abemaciclib for locally advanced or metastatic estrogen receptor-positive/human epidermal growth factor receptor 2 negative breast cancer.

These data will be presented at the 2024 San Antonio Breast Cancer Symposium.

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 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.

Additional details on the TACTIVE-U poster presentation at SABCS are below:

Key findings included:

• There was no significant drug-drug interaction, and data reflected vepdegestrant has no clinically meaningful effect on abemaciclib exposure.
• Encouraging preliminary antitumor activity is observed with a clinical benefit rate of 62.5% in all CBR-eligible patients (10/16), 62.5% in patients with mutant ESR1 (5/8), and 62.5% in patients with wild-type ESR1 (5/8).
• The objective response rate (ORR) in evaluable patients was 26.7% overall (4/15), 37.5% in patients with mutant ESR1 (3/8), and 14% in patients with wild-type ESR1 (1/7).

Arvinas and Pfizer continue to evaluate data from the ongoing TACTIVE-U clinical trial, including combinations of vepdegestrant plus abemaciclib, ribociclib, or samuraciclib.

Price Action: At the last check on Tuesday, PFE stock was down 1.70% at $25.66, and ARVN stock was down 1.30% at $24.76.

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