07:21 AM EDT, 06/02/2025 (MT Newswires) -- Arvinas ( ARVN ) and Pfizer ( PFE ) on Saturday reported results from a phase 3 clinical trial of vepdegestrant monotherapy versus fulvestrant in adults with a certain type of advanced or metastatic breast cancer.

Vepdegestrant showed a "statistically significant and clinically meaningful" improvement in progression-free survival among patients with an estrogen receptor 1 mutation, lowering the risk of disease progression or death by 43% versus fulvestrant, the companies said.

However, the trial didn't reach statistical significance in improvement in progression-free survival in the intent-to-treat population, with a median survival of 3.7 months for vepdegestrant, compared with 3.6 for fulvestrant, Arvinas ( ARVN ) and Pfizer ( PFE ) said.

Treatment-emergent adverse events leading to treatment discontinuation occurred in 2.9% of patients taking vepdegestrant versus 0.7% of patients on fulvestrant, the companies said.

Arvinas ( ARVN ) shares were down 6.9% in recent premarket activity Monday, while Pfizer ( PFE ) rose 0.4%.