CHICAGO, June 2 (Reuters) - An experimental cancer drug from Loxo Oncology performed even better in patients with a rare mutation of the RET gene than previously reported, according to updated results from an early stage clinical trial presented on Saturday.
Last month, Loxo released preliminary data that showed its drug, LOXO-292, targeting RET mutations shrank tumors in 69 percent of advanced cancer patients regardless of whether their disease originated in the lung, pancreas or thyroid. Loxo shares rose 20 percent on the news.
The new results, which included additional patients and more months of treatment, showed an overall response in 77 percent of those with RET fusion mutations who received the Loxo pill, researchers said on Saturday at the American Society of Clinical Oncology meeting in Chicago.
For more coverage of the meeting, see: here
The 77 percent was seen in patients whose RET gene was abnormally fused with another gene, driving cancer growth. In medullary thyroid cancer with a different type of RET mutation, LOXO-292 shrank tumors in 45 percent of patients.
"The activity was pretty impressive," said Dr. Alexander Drilon, the study's lead investigator from Memorial Sloan Kettering Cancer Center in New York. "To date, there is no drug approved for RET fusions or RET mutations."
Loxo attracted attention at last year's ASCO meeting with data showing that its drug larotrectinib shrank tumors in patients with more than a dozen different types of cancer all driven by a mutation known as TRK fusion.
Loxo's discoveries have highlighted the value of more widespread genomic testing of tumors to find the best treatment. Both the TRK and RET mutations are rare but occur in different types of cancer.
The company has since forged a partnership with Germany's Bayer and its stock price has quadrupled in value.
Larotrectinib is expected to be Loxo's first drug on the market, with Wall Street analysts forecasting eventual annual sales reaching $500 million to $1 billion. Earlier this week, U.S. drug regulators said it would receive an expedited review, with an approval decision likely by late November.
RET fusions occur in about 2 percent of lung cancers, 10 to 20 percent of papillary thyroid cancers, and a small number of other cancers. Activating RET point mutations account for about 60 percent of medullary thyroid cancers, which comprise 3 percent of all thyroid cancers.
The Loxo study showed early evidence of lasting benefit of its drug in RET-driven cancers, with about 90 percent of patients still on therapy as of an April cut-off, with the earliest patients still responding after 10 months.
Blueprint Medicines is developing a rival RET drug.
Drilon, who consults on RET-targeted drugs from both companies, said it was too early to determine which is better. "These trials started a year ago. It's not reasonable to say this or that about the Blueprint versus Loxo drug," he said.
Reporting by Julie Steenhuysen Editing by Bill Berkrot