What happened

After an abstract for its clinical-stage prostate cancer drug was released ahead of an upcoming presentation at the American Society of Clinical Oncology (ASCO) virtual annual meeting later this month, shares in Arvinas, Inc. (NASDAQ:ARVN) are tumbling. As of 12:15 p.m. EDT Thursday, shares are down 13.7%.

So what

The annual ASCO conference is one of the most highly anticipated events in healthcare. Biotech companies like Arvinas use the meeting to highlight progress toward developing more effective treatments, and often data presented at the conference can cause big swings in biopharma stock prices. As a result, abstracts outlining results to be presented at the conference are worth watching.

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The abstract released on Wednesday highlighted ARV-110, which is being developed as a treatment for metastatic castration-resistant prostate cancer. A once-daily androgen receptor (AR) protein degrading therapy that's taken orally, ARV-110 aims to tackle mCRPC by eliminating the body's ability to create proteins that contribute to tumor formation. The ARV-110 abstract includes results from an ongoing phase 1/2 study designed to evaluate safety risks to help researchers pick the correct dose to advance into larger studies.

The results so far show no evidence of clinical response below 140 mg, however, two patients in the 140 mg cohort saw a 50% or greater drop in prostate-specific antigen, a key disease marker. In the 280 mg cohort, two patients suffered elevated liver enzymes, with one case resulting in acute renal failure. Both patients were also taking Crestor, a statin used to treat high cholesterol, and after discontinuing Crestor in all patients, there weren't any additional reports of severe adverse events.

Now what

Prostate cancer is the second most common cancer in men, and mCRPC patients who have already progressed following two or more existing treatment options could benefit significantly from additional alternatives. Up to 25% of patients fail to respond to the most widely used hormone therapies in the indication, Johnson & Johnson's Zytiga and Pfizer's Xtandi, and most patients end up developing resistance to those drugs.

Investors appear to have been hoping for more people to respond to therapy, but efficacy wasn't the main goal of this study. Additionally, since the study is ongoing with a primary completion date in early 2021, it's likely there will be more data available in the coming year. Because the market opportunity is large and a response was seen in the 140 mg cohort, investors might want to keep Arvinas on their radar, particularly since data from another study evaluating protein degradation in breast cancer patients is anticipated prior to the end of 2020.