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MacroGenics touts a PhIII win in a head-to-head with best-seller Herceptin — shares rocket higher

MacroGenics $MGNX has claimed success in their Phase III trial of their drug margetuximab for metastatic breast cancer, putting them on the path to a BLA filing. But they’re not offering a lot of detail.

The top-line number cleared the bar for statistical significance, but not by a wide margin.

Scott Koenig

In a head-to-head with Herceptin (trastuzumab), the biotech reports that their drug won out in prolonging progression-free survival among heavily treated third- and fourth-line HER2+ patients. The p-value on the primary endpoint was 0.033 with a 24% risk reduction for disease progression. A much better score of 0.005, though, was recorded for the majority of patients in the trial who were carriers of the CD16A (FcγRIIIa) 158F allele, which is linked to resistance to Herceptin.

This was a closely watched catalyst for MacroGenics. Its shares shot up 166% on the top-line report Wednesday morning. Jonathan Chang at Leerink noted:

Many investors we have spoken with expected the study to be negative and we believe little value for Her2+ mBC was baked into the MGNX stock. We modeled a 60% probability of success.

We don’t know yet how those numbers translate to months of added PFS, or the overall survival rate. Researchers are still pondering OS. The more exact data, which will tell analysts a lot more about the market potential for this drug, will be unveiled at a later cancer conference.

Researchers will be taking the data from the SOPHIA study, which enrolled 536 patients, to regulators sometime in the second half of this year.

The company has been touting their antibody’s engineering, saying the better Fc domain can engage the immune system. The drug is designed to target the HER2 oncoprotein. And there’s a long way to go on the development effort.

“We look forward to additional opportunities to develop margetuximab in other HER2-positive breast and gastric cancer populations,” MacroGenics CEO Scott Koenig remarked. 

A side beneficiary in today’s news is Zai Lab, $ZLAB the Chinese biotech that in-licensed regional rights to the drug for a low upfront payment. Jefferies noted:

Recall, ZLAB in-licensed marge 12/2/18 for an upfront of $25M for rights to breast and gastric cancer in China (our note here). Expectations for the SOPHIA ph.III readout were low, and we believe ZLAB took a calculated risk/benefit approach w/ marge that led to best-case scenario, given today’s news.

The biotech hit a stumbling block at the end of last year. Leery about signs of liver toxicity among patients taking a B7-H3 × CD3 bispecific under development at MacroGenics, the FDA slapped a partial hold on the early-stage program.


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Research Scientist - Immunology
Recursion Pharmaceuticals Salt Lake City, UT
Director of Operations
Atlas Venture Cambridge, MA

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