What happened

Shares of MacroGenics (MGNX -5.24%) were tumbling 5.7% lower as of 11:39 a.m. EDT on Thursday. The decline came after the company announced preliminary results from its phase 1 study evaluating MGC018 in treating solid tumors.

So what

MacroGenics said that it saw preliminary signals of anti-tumor activity with MGC018 in treating patients with advanced metastatic castration-resistant prostate cancer (mCRPC). The company reported that reductions in prostate-specific antigens (PSAs) of at least 50% were observed in five patients. Of the nine patients in the study with mCRPC, eight demonstrated stable disease. 

Man in a lab coat looking through a microscope with a woman in a lab coat standing in the background.

Image source: Getty Images.

The company also stated that three patients with melanoma were given a 4.0 mg/kg dose of MGC018. One of these patients had a confirmed partial response with a 36% target lesion sum reduction.

MacroGenics reported that blood and skin toxicities related to MGC018 have been "clinically manageable." In the dose-escalation part of the phase 1 study, 27 of the 29 patients experienced at least one treatment-related adverse event. 

Investors seem to have hoped for better results based on the performance of the biotech stock today.

Now what

MacroGenics now plans to share the full data from its phase 1 study of MGC018 at the American Society of Clinical Oncology annual meeting in early June. The company also expects to provide additional updates at other scientific conferences.