What happened

Shares of oncology-focused biotech Mirati Therapeutics (MRTX) have stumbled across the past few days, with the stock trading in the red by nearly 11% week to date as of Thursday's close. A spot of good news from a product that rivals its key pipeline drug seemed to be the force pulling down Mirati's shares.

So what

On Monday, Mirati's large and powerful peer Amgen (AMGN 2.29%) announced it had received conditional marketing authorization from the European Commission for its drug Lumykras to treat advanced non-small cell lung cancer (NSCLC) with the KRAS G12C (a protein) mutation in adults.

Two face-masked medical researchers having a discussion at a laboratory table.

Image source: Getty Images.

That was an unambiguous win for Amgen, and certain investors considered it also a blow to Mirati. This is because the latter company's leading pipeline program, adagrasib, also targets cancers with KRAS mutations.

Adagrasib, which is being evaluated both as a monotherapy and in combination with other drugs, has not yet won any approvals or authorizations. Last November, Mirati began a New Drug Application (NDA) with the Food and Drug Administration (FDA) for it in the treatment of patients afflicted by previously treated NSCLC with the mutation.

Now what

The drug has tested well in its clinical trials for more than one indication, a fact that Mirati was quick to tout when announcing the NDA submission. At the time, the biotech quoted its CEO David Meek as saying, "Our recent positive clinical updates for adagrasib reinforce a best-in-class profile, including topline results from the registration-enabling Phase 2 cohort of the KRYSTAL-1 study in patients with KRAS G12C-mutated lung cancer ... as well as encouraging results in KRAS G12C-mutated colorectal and pancreatic cancers."

Adagrasib is also to be put through its paces as an NSCLC therapy in combination with investigational drugs from Sanofi and Verastem Oncology, as a result of research collaboration deals agreed by Mirati late last year.