MacroGenics Inc. (NASDAQ: MGNX) shares absolutely exploded on Wednesday after the firm announced late-stage results for its breast cancer trial. Specifically, the firm reported Phase 3 results from its clinical study of margetuximab in HER2-positive metastatic breast cancer patients.

Although shares more than doubled in the session, the stock is still was not that close to its 52-week high.

For some quick background: margetuximab is an investigational immune-enhancing monoclonal antibody derived from the company’s proprietary Fc Optimization technology platform.

The Sophia clinical trial met the primary endpoint of prolongation of progression-free survival (PFS) in patients treated with the combination of margetuximab plus chemotherapy compared to trastuzumab plus chemotherapy.

Patients in the margetuximab arm experienced a 24% risk reduction in PFS compared to patients in the trastuzumab arm. Notably, about 85% of patients in the study were carriers of the CD16A (FcγRIIIa) 158F allele, which has been previously associated with diminished clinical response to Herceptin and other antibodies. In this pre-specified subpopulation, patients in the margetuximab arm experienced a 32% risk reduction in PFS compared to patients in the trastuzumab arm.

Follow-up for determination of the impact of therapy on the sequential primary endpoint of overall survival is ongoing, as pre-specified in the study protocol and recommended by the trial’s independent Data Safety Monitoring Committee. MacroGenics anticipates submitting a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) in the second half of 2019.

Hope S. Rugo, M.D., Director, Breast Oncology and Clinical Trials Education, University of California San Francisco Comprehensive Cancer Center, commented:

There are currently no approved agents for the treatment of patients with metastatic HER2+ breast cancer who have previously received trastuzumab, pertuzumab and ado-trastuzumab emtansine. If margetuximab is approved, based on SOPHIA data, I believe that this agent could become a valuable treatment option for these patients.

Shares of MacroGenics were last seen up about 165% at $29.45 on Wednesday, in a 52-week range of $9.87 to $32.74. The consensus analyst price target is $29.55.

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