MacroGenics' Vobra Duo Safety Profile Declines Sharply

MacroGenics' experimental drug, vobramitamab duocarmazine (vobra duo), has recently faced significant safety concerns following the latest data cut from the ongoing Phase II TAMARACK study. This recent update revealed five fatalities among patients, a stark contrast to last month's report which indicated no deaths in the trial involving metastatic castration-resistant prostate cancer (mCRPC) patients. The news led to a dramatic 62% plunge in the company's shares.

Upon closer examination, MacroGenics clarified that two of the deaths—one due to acute myocardial infarction and the other from cardiac arrest—were deemed unrelated to the experimental drug. However, the remaining fatalities included two cases of pneumonitis, which may be treatment-related, and a Grade 3 pleural effusion. The latter is recorded as a fatal outcome and is currently under further investigation.

Breaking down the details, one death occurred in the patient group receiving a lower dose of vobra duo, whereas the other four fatalities took place among those administered the higher dose. The data also highlighted that 52.8% of patients treated with vobra duo experienced severe treatment-emergent adverse events (Grade ≥3). This led to 47.2% of patients requiring a dose reduction, and 13.1% discontinuing treatment altogether.

From an efficacy standpoint, the results showed that a confirmed prostate-specific antigen (PSA) reduction of at least 50% was achieved by 43.9% of patients in the low-dose group. In contrast, this figure dropped to 36.6% for those on the higher dose. Additionally, the confirmed objective response rate (ORR) stood at 17.8% for the low-dose group and 25% for the high-dose group. Prior to this data release, BMO Capital Markets analysts had anticipated that at least 50% of patients in the TAMARACK study would experience a PSA reduction of 50% or more, with an ORR ranging between 30% and 40%.

Despite these safety issues, MacroGenics' CEO, Scott Koenig, remains optimistic about the drug's potential. He stated, "As we view the data right now, both doses are potentially usable and further developable going forward with this interim data." Koenig also mentioned that planning activities for a potential Phase III study have already been initiated, with the possibility of it commencing next year.

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