MacroGenics drops further after halting Phase II due to safety issues

MacroGenics has ceased further patient dosing in its Phase II TAMARACK trial involving the antibody-drug conjugate (ADC) vobramitamab duocarmazine (vobra duo) after reporting five patient deaths. The company first exposed safety concerns in May, causing a substantial 77% drop in its share price. Following an update late Tuesday, the stock suffered an additional 28% decrease on Wednesday.

The TAMARACK study had enrolled 143 patients with metastatic castration-resistant prostate cancer (mCRPC) to receive increasing doses of vobra duo, which targets the tumor antigen B7-H3. Among the five fatalities, two deaths were possibly linked to the treatment and were caused by pneumonitis. Another death was due to a Grade 3 pleural effusion, which is still under investigation. The remaining two deaths were not deemed related to the experimental therapy.

After reviewing the TAMARACK data and consulting with the Independent Data Monitoring Committee, MacroGenics decided to discontinue the trial for the remaining participants who might have required additional doses. These participants will continue to be monitored for any new adverse events, as well as for disease progression and overall survival.

CEO Scott Koenig emphasized that patient safety is the company's primary concern. Having met the study’s primary endpoint, the decision was made to stop further dosing for the remaining participants who had not finished their treatment. Koenig mentioned that the company anticipates having sufficient data later this year to determine the next steps for the vobra duo program.

MacroGenics plans to present the TAMARACK study results at the European Society for Medical Oncology (ESMO) annual meeting in September. This presentation will include data on the primary endpoint of six-month radiographic progression-free survival (rPFS). The collected data will guide the company in designing future studies for vobra duo.

Koenig reaffirmed the company's commitment to thoroughly evaluating the potential of vobra duo in mCRPC by rigorously analyzing the data, including the mature median rPFS and overall survival outcomes.

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