Shares of Mirati Therapeutics Inc. fell Monday, Oct. 22, after the drug developer released a progress report of an early stage clinical trial of its lung cancer drug.

Shares of Mirati Therapeutics Inc. (MRTX - Get Report) fell Monday, Oct. 22, after the drug developer released a progress report of an early stage clinical trial of its lung cancer drug used in conjunction with a Bristol-Myers Squibb Co. (BMY - Get Report) medication.

Shares were down more than 15% at the Monday close.

The San Diego-based cancer-drug developer revealed some positive progress Monday on its phase 2 trial of sitravatinib used with Bristol-Myers' Opdivo, also know as nivolumab.

The ongoing study is evaluating the efficacy and safety of the two treatments in patients with non-small-cell lung cancer who previously underwent immune checkpoint inhibitor treatment.

Of the 56 patients, 45 saw their tumors shrink somewhat, with 18 of them seeing their tumors reduce in size by 30%. The total response rate was unclear, however, with 16 patients showing some level of response, but only 9 confirmed.

Mirati said the drug combination had so far been "well tolerated."

"The results of the study are encouraging as it continues to show a clinical benefit for these patients and has a favorable safety profile," said Ticiana Leal, an assistant professor of medicine at the University of Wisconsin, in a press release. "To date, the combination of sitravatinib and nivolumab has demonstrated a significant number of durable responses."

A phase 3 trial is planned for the first half of 2019.

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