An experimental breast cancer treatment co-developed by Pfizer and Arvinas significantly improved the time some patients lived without the disease worsening, but failed to achieve statistically significant results in others in a late-stage study.

Pfizer (NYSE:PFE) stock and Arvinas (NASDAQ:ARVN) stock slip in reaction to mixed Phase 3 data for their breast cancer drug vepdegestrant. Read more here.

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

Pfizer and Arvinas' experimental breast cancer treatment failed to delay the progression of the disease in a broader group of patients in a late-stage trial, sending the Connecticut-based biotech's shares down 36% before the bell.