Mirati Therapeutics Inc. shares dropped 19.5% in extremely heavy Monday morning trade after the company presented results from a phase 2 trial in which its cancer drug sitravatinib was combined with Bristol-Myers Squibb Co.’s cancer drug Opdivo . The trial enrolled patients with non-small cell lung cancer who had their cancer progress while taking a type of cancer drug called an immune checkpoint inhibitor. As of late August, of 56 patients in the trial who could be evaluated, 9 had a confirmed partial or complete response, the company said. Two additional patients had unconfirmed partial or complete responses — which are awaiting confirmation — and five others had unconfirmed responses “that will not be confirmed,” Mirati said. The company said that in total, 16 patients had partial or complete responses, including the latter two categories of patients in its count. The company also said that 18 patients had tumor reductions of more than 30%, and an early estimate of median duration response was more than nine months. Mirati plans a phase 3 randomized clinical trial comparing a combination of the two cancer drugs with the chemotherapy docetaxel. Bristol-Myers’ Opdivo is a checkpoint inhibitor that has already been approved in non-small cell lung cancer. As part of a major trend over the last several years, drugmakers have been testing immuno-oncology drugs like sitravatinib in combination with other cancer drugs, hoping that they might be more effective together. Mirati shares have dropped 41.5% over the last three months to $32.21, compared with a 1.6% slump in the S&P 500 and a 1.1% rise in the Dow Jones Industrial Average .