What happened

Shares of Mirati Therapeutics (NASDAQ:MRTX), a clinical-stage biopharmaceutical company with an oncology focus, are on the rise following a presentation from Amgen (NASDAQ:AMGN). Mirati investors were happy to see the industry giant report encouraging data from a new drug candidate similar to one that Mirati is developing, and have pushed the stock up 36.2% as of 11:57 a.m. EDT on Monday.

So what 

After Mirati's lead candidate, sitravatinib, disappointed investors late last year, the company is depending heavily on a candidate licensed from Array Biopharma (NASDAQ:ARRY) called MRTX849. This is a small-molecule drug that stops mutated KRas proteins from signaling for rapid growth and cell division.

Happy investor surrounded by falling banknotes.

Image source: Getty Images.

Investigators have been trying to inhibit out-of-control KRas proteins from promoting tumor growth for decades without success because the protein presents a target that's particularly difficult to reach. Another drug aimed at reducing KRas protein production from AstraZeneca and Ionis Pharmaceuticals failed its first human proof-of-concept study recently, and investors were worried that the whole KRas class was doomed.

Mirati's stock is on the rise today because Amgen's KRas inhibitor, called AMG 510, performed well enough to suggest Mirati is on the right track as well. AMG 510 helped shrink tumors for five out of 10 lung cancer patients. Of the 18 patients with colorectal cancer, 13 achieved stable disease. It's important to point out that these were relapsed patients who had already been through a wringer involving at least two rounds of standard treatment.

Now what

Mirati doesn't have any past successes to boast about, but the company that discovered MRTX849 sure does. Array Biopharma has produced more than one successful cancer treatment and recently proved it can design small-molecule drugs that can inhibit difficult targets with high specificity. 

Earlier this year, Eli Lilly (NYSE:LLY) bought Loxo Oncology for $8 billion after another small-molecule, Loxo, licensed from Array performed better than expectations. That doesn't necessarily mean that MRTX849 is destined to succeed as well, but investors will make this association until it's disproved by trial results.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.