(Corrects Blueprint data in paragraph 12 to reflect updated results presented at a medical meeting)
By Julie Steenhuysen
CHICAGO, May 16 (Reuters) - An experimental Loxo Oncology Inc drug that targets cancers with mistakes in the RET gene led to tumor shrinkage in nearly 70 percent of patients regardless of where their cancer originated, according to preliminary data from a small study released on Wednesday.
The drug, LOXO-292, was well tolerated by patients with advanced cancer, many of whom were resistant to or no longer being helped by available treatments, researchers reported.
Loxo shares rose more than 9 percent after the data was released, while shares of Blueprint Medicines, which is developing a rival drug, fell more than 12 percent.
The oral medicine is intended for cancer patients with RET abnormalities in which two genes become fused together, triggering accelerated cancer cell growth.
RET fusions, an acquired rather than inherited gene defect, occur in about 2 percent of lung cancers, 10 to 20 percent of papillary thyroid cancers, and a small number of other cancers. Other mutations known as activating RET point mutations account for about 60 percent of medullary thyroid cancers, which comprise 3 percent of all thyroid cancers.
As of the cutoff date of January 5, data included 35 patients with RET fusion positive tumors, including 27 with non-small cell lung cancer (NSCLC), 7 with papillary thyroid cancer and 1 with pancreatic cancer. Another 20 patients had medullary thyroid cancers with RET point mutations.
In RET fusion positive patients, 69 percent of those who could be evaluated had significant tumor shrinkage, based on standard criteria for overall responses, typically shrinkage by at least a third.
The overall response rate was 65 percent for those with NSCLC, including three whose cancer had spread to the brain, and 83 percent for patients with papillary thyroid cancer.
In patients with medullary thyroid cancers, some 79 percent experienced tumor shrinkage ranging from 9 to 45 percent.
A brief summary of the results was released on Wednesday ahead of next month's American Society of Clinical Oncology Meeting Chicago, where more detailed data on the study involving more patients will be presented.
Loxo Chief Executive Josh Bilenker, in a call with analysts earlier this month, said he was "encouraged by the data we submitted in January," but noted that efficacy has improved since January.
The findings follow initial results released at a cancer meeting last month by Blueprint, whose rival RET-targeted drug showed an overall response rate of 45 percent, including 50 percent for NSCLC and 40 percent for medullary thyroid cancers.
Of the 57 patients in the Loxo study, 52 remained on the treatment. Side effects were mostly minor and occurred in about 10 percent of patients. They included fatigue, diarrhea and shortness or breath. (Reporting by Julie Steenhuysen; edited by Bill Berkrot)