What happened

Shares of Mirati Therapeutics (NASDAQ:MRTX), a clinical-stage biopharmaceutical company, rose 27.9% in December, according to data from S&P Global Market Intelligence. Investors were revved up by results from an ovarian cancer study involving Mirati's sitravatinib plus tislelizumab, an anti-PD1 antibody from BeiGene (NASDAQ:BGNE).

So what 

Most of the attention directed at Mirati Therapeutics is focused on early clinical-stage testing of MRTX849, a KRAS-inhibitor that could end up treating cancer patients with a variety of solid tumors. Sitravatinib's a kinase inhibitor in a late clinical-stage study with Opdivo, a PD1 inhibitor from Bristol-Myers Squibb (NYSE:BMY) that Bristol didn't seem interested in following lackluster mid-stage trial results.

A smiling woman raises her arms in celebration, with an upward-trending arrow behind her on the wall.

Image source: Getty Images.

Mirati's stock rose in December thanks to fairly positive results from an ovarian cancer trial with sitravatinib plus tislelizumab. At the data cutoff in July, the combination shrank tumors for seven out of 17 evaluable ovarian cancer patients that had already relapsed following treatment with standard chemotherapy.

Since Bristol's Opdivo and BeiGene's tislelizumab act the same way, results from the combination study could breathe new life into Mirati's partnership with Bristol-Myers as well as Beigene.

Now what

Investors need to remember that instead of sponsoring sitravatinib's pivotal trial in return for a share of its potential sales, Bristol-Myers agreed to provide free Opdivo, and that's all. That's troubling because in the past, Bristol-Myers has shoveled money toward collaboration partners that might be able to boost Opdivo's addressable patient population. 

In 2020, Mirati shares have already given back most of the gains posted in December pulling its market cap down to $4.5 billion at the moment. This figure could rise significantly on the back of further success from its KRAS inhibitor, MRTX849, but sitravatinib's best days have passed.