Microscopic view of pancreatic cancer cells.
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An experimental drug from Mirati Therapeutics that targets a specific genetic mutation significantly reduced the tumor size in 40% of patients with advanced lung and colon cancer so far evaluated in a small, early phase study, researchers said Monday.  Investors have been keen to see how Miratis data stacks up against results for a similar drug, AMG51
Of 17 patients enrolled in the Phase 1 trial of Mirati's oral drug MRTX849, 12 were evaluated, including six with lung cancer and four with colon cancer.
Three of the lung cancer patients had a "partial response", defined as a 30% or greater reduction in tumor size. One of the evaluated colon cancer patients also had a partial response.
The lung cancer responses are considered "unconfirmed" since patients have not had follow-up scans.
"The signs are there, but the number is low," Investigator Dr. Pasi Janne, director of thoracic oncology at Boston's Dana-Farber Cancer Institute, told Reuters. "It is too early to say anything about the durability of the response."
All responding patients received the highest dose used in the dose-varying study – 600 milligrams given twice a day, he said.
Cancer was stabilized in the other evaluated patients, including two with cancer in the attachment, Janne said, although cancer in one trial patient was exacerbated.
Janne said the side effects of MRTX849 have been most mild, including diarrhea and nausea, but two patients had higher grade toxicity including increased levels of pancreatic enzymes, although they did not show any symptoms of pancreatitis.
The first human results were presented in Boston at the International Conference on Molecular Targets and Cancer Therapeutics.
Amgen has reported phase 1 study results that showed that tumors shrunk in approximately half of advanced lung cancer patients given a daily dose of 960 mg AMG510, but the response rate for colon cancer has been much lower. U.S. The Food and Drug Administration has provided a firm track record of AMG510 for lung cancer.