Pharma giant Pfizer and Arvinas’s human epidermal growth factor receptor 2 (HER2) negative breast cancer therapy, vepdegestrant, has seen mixed results after it was only able to extend progression-free survival (PFS) in certain patients in a Phase III trial.

The drug in question, called vepdegestrant, is an oral PROteolysis TArgeting Chimera (PROTAC) ER degrader. The phase 3 study assessed vepdegestrant against AstraZeneca’s hormone med Faslodex in 624 patients with ER+/HER2- advanced or metastatic breast cancer who had already tried CDK 4/6 inhibitors and endocrine therapy.

Wedbush became the latest brokerage to downgrade Arvinas (NASDAQ:ARVN) on Wednesday after the company posted underwhelming late-stage trial data for vepdegestrant, an experimental breast cancer therapy it co-develops with Pfizer (NYSE:PFE).

Arvinas stock lost half its value Tuesday after the biotech company reported mixed results from its Pfizer-partnered breast cancer drug.