June 4 (Reuters) - Women with advanced breast cancer who carry specific genetic mutations experienced double the response rate and delayed disease progression when treated with AstraZeneca Plc's Lynparza compared with standard chemotherapy, according to data from a late-stage trial presented on Sunday.
In the study of 302 patients with inherited mutations of the BRCA1 or BRCA2 genes, about 60 percent who received the oral treatment Lynparza experienced significant tumor shrinkage compared with 29 percent who got chemotherapy. Nine percent of Lynparza patients had a complete response versus 2 percent on chemotherapy.
Median time to disease worsening was seven months with Lynparza versus 4.2 months for chemotherapy, a statistically significant 42 percent reduction in progression risk.
In addition, "there was a delay in the time until their quality of life began to deteriorate," said Dr Mark Robson of Memorial Sloan Kettering Cancer Center in New York, who led the study.
Women in the study had metastatic breast cancer classified as hormone receptor-positive or triple negative and had undergone prior chemotherapy.
"Triple negative breast cancer in particular is difficult to treat after it's failed a couple of chemotherapy regimens. To have a relatively well-tolerated oral agent as an alternative for these women is certainly exciting," said Robson, who presented the data at the American Society of Clinical Oncology (ASCO) meeting in Chicago.
Lynparza, known chemically as olaparib, belongs to a class of drugs called PARP inhibitors already approved for ovarian cancer.
Michelle Werner, head of U.S. oncology for AstraZeneca, said the data represents "the first time that a PARP has demonstrated benefits outside of the ovarian cancer space."
The company expects to seek approval for use of the drug in breast cancer toward the end of this year, she said.
"I'm convinced PARP inhibitors are here to stay in breast cancer," said ASCO President Dr Daniel Hayes, who was not involved in the study.
About 3 percent of breast cancers occur in people with inherited BRCA1 or BRCA2 mutations that lower a cell's ability to repair damaged DNA. Up to 65 percent of women who inherit the mutations will develop breast cancer, often much younger than is typical for the disease.
Serious side effects were reported in 37 percent of Lynparza patients compared with 50 percent for chemotherapy, but just 5 percent discontinued Lynparza due to side effects.
Robson said the AstraZeneca drug should be tested in combination with a variety of other therapies to assess if they "can improve the responses and extend the benefit." (Reporting by Bill Berkrot in New York; Editing by Matthew Lewis)