Mirati drug shrinks tumors in some cancer patients in early-stage trial

(Reuters) - An experimental drug from Mirati Therapeutics Inc that targets a specific genetic mutation significantly reduced tumor size in 40% of patients with advanced lung and colorectal cancer so far evaluated in a small, early-stage trial, researchers said on Monday.

Investors have been keen to see how Mirati’s data stacks up against results for a similar drug, AMG510, under development by Amgen Inc. Both target a mutated form of a gene known as KRAS that occurs in around 13% of non-small cell lung cancer cases, 3-5% of colorectal cancers and up to 2% of other solid tumor cancers.

Out of 17 patients enrolled in the Phase 1 trial of Mirati’s oral drug MRTX849, 12 have been evaluated, including six with lung cancer and four with colorectal cancer.

Three of the lung cancer patients had a “partial response,” defined as a 30% or more reduction in tumor size. One of the evaluated colorectal 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 numbers are small,” lead study 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 response.”

All of the responding patients received the highest dose used in the dose-ranging study - 600 milligrams given twice a day, he said.

Cancer was stabilized in the other evaluated patients, including two with cancer of the appendix, Janne said, although one trial patient’s cancer worsened.

Janne said side effects of MRTX849 have been mostly mild, including diarrhea and nausea, but two patients had higher-grade toxicity including increased levels of pancreatic enzymes, although they did not exhibit any symptoms of pancreatic inflammation.

The first-in-human results were presented in Boston at the International Conference on Molecular Targets and Cancer Therapeutics.

Amgen has reported Phase 1 trial results showing that tumors shrank in about half of advanced lung cancer patients given a 960 mg daily dose of AMG510, but the response rate in colon cancer has been much lower. The U.S. Food and Drug Administration has granted “fast track” status to AMG510 for lung cancer.

Reporting by Deena Beasley; Editing by Tom Brown