What happened

Shares of small-cap cancer specialist MacroGenics (MGNX 2.68%) rose by as much as 190.9% in early morning trading today on over 36 times the normal daily volume. The stock is soaring in response to a positive late-stage readout for the company's HER2-positive breast cancer treatment candidate, margetuximab. According to the press release, patients treated with a combination of margetuximab and chemotherapy demonstrated a statistically significant improvement in progression-free survival (PFS) compared to those receiving Roche's Herceptin plus chemotherapy.

Although the biotech's shares have given back some of the enormous gains from the beginning of today's trading session, MacroGenics stock was still up by whopping 131% as of 11:50 a.m. EST. 

Female cancer patient staring out of a window in an all-white room

Image source: Getty Images.

So what

Interestingly enough, MacroGenics shares were actually moving lower heading into this pivotal data readout. Prior to today's enormous jump, for instance, the biotech's stock was down by a noteworthy 12.5% for the year. The core issue was that Wall Street apparently didn't think that margetuximab had much of a chance of besting Roche's all-star cancer drug in this head-to-head matchup. Citi analyst Yigal Nochomovitz downgraded the stock only a few days ago due to concerns that margetuximab would fail to improve PFS in this trial. 

Now what

With this positive trial readout in hand, MacroGenics plans on filing for the drug's approval with the U.S. Food and Drug Administration in the second half of this year. And if approved, margetuximab should go on to become a tremendous growth driver for the company in the years ahead. This particular breast cancer market, after all, could be worth as much as $10 billion in annual sales by 2025, according to a report by GlobalData. That amount dwarfs MacroGenics' current market cap of approximately $1 billion -- implying that there could be considerably more upside to come.

Check out the latest MacroGenics earnings call transcript.