What happened

Shares of Mirati Therapeutics (MRTX), a clinical-stage biopharmaceutical company, are rising again today. This time, the stock is soaring in response to highly anticipated clinical trial data produced by Mirati, instead of by a similar program from Amgen (AMGN -0.50%). Investors who are relieved that Mirati's experimental cancer drug MRTX849 performed arguably better than Amgen's AMG 510 pushed the stock 15% higher as of 11:49 p.m. EDT on Tuesday.

So what 

A mutated KRAS gene was one of the first gene-specific drivers of tumor growth elucidated by researchers decades ago. Unfortunately, KRAS proteins have a relatively smooth shape that has made them impossible to inhibit, until recently.

Man in a suit looking up at an upward sloping chart.

Image source: Getty Images.

Earlier this year, Amgen presented initial results from a trial with its KRAS inhibitor, AMG 510, that impressed investors and pushed up Mirati stock in the process. Mirati's climbing again today because the company presented phase 1 results from its own KRAS inhibitor, MRTX849, and it appears competitive with Amgen's. The highest dosage tested shrank tumors for three out of five evaluable lung cancer patients and one out of two colon cancer patients.

Now what

It's really not a good idea to compare results from two different populations, but without a head-to-head study, it's all we have to work with. In September, Amgen's AMG 510 lost some of its luster after the company showed it shrank tumors for just one colon cancer patient out of 12 who received the highest dosage tested. Among 13 evaluable lung cancer patients who received the highest dosage, researchers measured tumor shrinkage in seven.

It's important to point out that studies run by Amgen and Mirati enrolled patients who hadn't responded or relapsed after several previous lines of treatment. Getting any of these patients to respond to a new therapy is a noteworthy achievement. At the moment, though, it looks like Mirati has a better candidate.

An estimated 14% of lung cancer patients and perhaps 4% of colon cancer patients have tumors driven by the KRAS mutation that MRTX849 targets. If Mirati Therapeutics can continue producing results that perform as well or better than Amgen, the company's $3.7 billion market cap at recent prices could swell to several times its size and make Mirati one of the best performing biotech stocks in the years ahead.