AstraZeneca PLC's Lynparza, already approved as an ovarian cancer treatment, was shown to benefit breast cancer patients in a trial presented June 4 at the annual meeting of the American Society of Clinical Oncology, or ASCO.
Treating certain breast cancer patients with Lynparza reduced their risk of death from the disease or tumor progression by 42% compared to chemotherapy in the phase 3 trial, the company said. Phase 3 is usually the last stage of human testing required for regulatory approval.
The data will form the basis of a filing with the U.S. Food and Drug Administration later this year to expand the drug's use outside of ovarian cancer, where it last year earned $218 million, Michelle Werner, AstraZeneca's vice president of U.S. oncology, said in an interview.
Lynparza is one of three so-called PARP inhibitors on the market, alongside Tesaro Inc.'s Zejula and Clovis Oncology's Rubraca. By blocking the PARP enzyme within cancer cells, the drugs hinder their ability to repair damaged DNA, leading to cell death, according to the National Cancer Institute.
"It's the first time we've been able to demonstrate the potential benefits of PARP inhibition outside of ovarian cancer," Werner said. "We haven't yet seen that with any of the other PARP inhibitors."
AstraZeneca previously disclosed that the trial had positive results. The latest release reveals the magnitude of the benefits.
An improvement in progression-free survival of three months or greater would be "clinically relevant," Leerink equity analyst Michael Schmidt said in a May 30 analyst note, citing an interview with an expert physician.
By that measure, Lynparza came close. It produced a median progression-free survival of seven months, compared to 4.2 months among those who received standard chemotherapy treatments.
The drug also performed well on a variety of secondary endpoints, according to Werner. It achieved a 59.9% objective response rate, compared to 28.8% in the chemotherapy arm. In addition, patients receiving Lynparza were able to stay on the medication longer before progressing to second-line therapy than those who received chemotherapy, according to the study abstract.
The rate of severe or life-threatening side effects was 36.6%, compared to 50.5% of patients in the chemotherapy arm.
Lynparza is the first PARP inhibitor drug to demonstrate an efficacy benefit over an active comparative, Werner said.
But Leerink's Schmidt noted that the trial only compared Lynparza to non-platinum-based chemotherapy, even though platinum-based chemotherapy typically has better efficacy in the trial's patient population.
Specifically, the trial tested the subset of breast cancer patients who inherited a deleterious BRCA mutation and whose cancer tested negative for the HER2 protein.
"Much of the innovation that we've seen in recent years has been in the HER2-positive or HER2-targeted patient population, and that's why the HER2-negative patient population hasn't really been able to benefit from any of those new innovations," Werner said.
AstraZeneca is planning or conducting other studies to further increase use of Lynparza to treat earlier-stage breast cancer, as well as other cancers such as those of the pancreas and prostate, Werner said. She added that combination therapies involving Lynparza are also possible in the future.
The results of the latest trial will be discussed further during an afternoon plenary session of the ASCO cancer conference.