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

The company is working on a protein degrader. These drugs use the body's natural mechanism for destroying proteins, dragging problematic targets to the body's molecular garbage disposal. In this case, the Arvinas drug degrades the estrogen protein driving patients' breast cancer.

Patients who received the experimental drug, vepdegestrant, lived longer before their disease worsened — a bar called progression-free survival — than those given fulvestrant. Fulvestrant is an approved antiestrogen injectable drug, while vepdegestrant is a pill.

But the results in the intent-to-treat group didn't reach statistical significance. Intent-to-treat includes all patients who received the drug, regardless whether they adhered to or finished treatment.

In morning trades, Arvinas stock collapsed more than 50% to 8.60. Pfizer stock also fell 1.5% to 26.24.

Arvinas Stock: Overall Survival Is Key

Arvinas tested its drug in patients with a mutated estrogen receptor and those without — respectively, ESR1mt and ESR1wt. The latter group has the same type of breast cancer, but without the same genetic mutation driving it.

"While the press release did not disclose ESR1wt efficacy, the failure of the (intent-to-treat) analysis suggests that ESR1wt patients likely did not benefit meaningfully from (vepdegestrant)," Leerink Partners analyst Andrew Berens said in a report.

Notably, Arvinas said it didn't have the results of overall survival, a marker for how long patients lived before dying of any cause.

Still, Berens kept his outperform rating on Arvinas stock.

"We think that there could be potential to convince the (Food and Drug Administration) that a non-injectable alternative to fulvestrant with non-inferior efficacy should be approved, even in the broader population, as long as (overall survival) eventually trends favorably," he said.

Shares Tumble To Record Low

But Arvinas stock fell to a record low Tuesday. Shares are now well off their 50-day and 200-day moving averages, MarketSurge shows.

Arvinas shares also have a poor IBD Digital Relative Strength Rating of 10, which puts them in the lowest 10% of all stocks when it comes to 12-month performance.

Pfizer stock slightly undercut its 50-day line, but shares are still consolidating with a buy point at 31.54.

Follow Allison Gatlin on X/Twitter at @AGatlin_IBD.

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