(CNN) An experimental prostate cancer therapy may change the way patients are treated for the second-deadliest cancer in men.
In a "landmark" phase III clinical trial, presented at the European Society of Medical Oncology conference in Barcelona on Monday, the drug olaparib was shown to be safe and effective in delaying the progression of disease in men with both metastatic castrate-resistant prostate cancer and mutations in their homologous recombination repair, or HRR, genes.
Castrate-resistant prostate cancer means that the cancer keeps growing even when the amount of testosterone in the body has been reduced to very low levels. HRR genes include the BRCA1 and BRCA2 genes, as well as others known to raise the risk of certain cancers.
"This is a landmark trial and potentially practice-changing for men with advanced metastatic castration-resistant prostate cancer -- the deadly phase of the disease," said Dr. Maha Hussain, deputy director of the Robert H. Lurie Comprehensive Cancer Center at Northwestern University Feinberg School of Medicine in Chicago and first author of the trial.
"These are pre-treated patients who have failed several previous lines of therapy and therefore are unfortunately already very ill and their cancer is deadly," she said. "Olaparib achieved a significant and clinically meaningful improvement in the time men lived without progression of their cancer -- an average that is more than double, in fact. This is a huge advancement."
Olaparib, which is sold under the brand name Lynparza, is a prescription medication that is already used to treat adults with certain cancers, including ovarian, fallopian tube or primary peritoneal cancer, and certain types of breast cancer. The drug works by targeting and killing cancer cells.
Now, the pharmaceutical company AstraZeneca -- which manufactures olaparib -- said the hope is to get this treatment approved "as soon as possible" for prostate cancer, the second leading cause of cancer death in men in the United States.
The trial involved administering either olaparib, a type of targeted cancer therapy, or other drug treatments to patients with castration-resistant prostate cancer and HRR gene mutations. The trial included 387 patients and was funded by AstraZeneca and Merck Sharp & Dohme Corp., a subsidiary of Merck.
"Here's the special thing about these patients: They were tested for the presence of that mutation, and that mutation had to be found in the tumor. So the test was done in a tumor sample," said Dr. Eleni Efstathiou, associate professor of genitourinary medical oncology at MD Anderson Cancer Center in Houston, who spoke about the trial at the conference on Monday.
The trial found that in the prostate cancer patients with BRCA1, BRCA2 or ATM gene mutations, olaparib improved the amount of time they lived without disease progression to an average 7.4 months, compared with 3.6 months among those treated with one of the currently-used drugs: hormone therapy enzalutamide, sold under the brand name Xtandi, or the hormone-based chemotherapy abiraterone, sold under the brand name Zytiga.
The most common adverse events associated with treatment in the study were anemia, nausea, decreased appetite and fatigue.
"What is important is that this is the first-ever trial in prostate cancer to be a targeted trial, to actually look for a treatment effect for therapy patients with a drug that targets a specific molecular pathway -- a specific mutation," Efstathiou said. "We never had such a trial in prostate cancer to deliver positive results."
In 2016, olaparib was granted a "breakthrough therapy" designation by the US Food and Drug Administration to be studied for the treatment of castration-resistant prostate cancer associated with BRCA1, BRCA2 or ATM gene mutations, according to AstraZeneca.
A breakthrough therapy designation means the development and review of a drug intended to treat a serious condition can be expedited.
This research comparing olaparib vs. enzalutamide or abiraterone has been called the PROfound study.
"PROfound is a landmark trial for patients with advanced prostate cancer who have progressed after hormonal therapy. Lynparza (olaparib) will be not only a much needed practice-changing therapy but is the first to unveil the promise of targeted therapies against genomic alterations in this disease," Dr. José Baselga, executive vice president of research and development oncology at AstraZeneca, said in an email on Monday.
The company said that it is too early to say how much olaparib for the treatment of prostate cancer would cost, as it first would need FDA approval.
Most people think of BRCA gene mutations as being tied to breast and ovarian cancer, but researchers have long known that several cancers other than breast and ovarian are associated with harmful mutations in BRCA1 and BRCA2 genes, including prostate cancer.
"We've known for some time that BRCA mutations play a role in prostate cancer and specifically an increased risk of developing prostate cancer and an increased risk of more aggressive prostate cancers," said Dr. Brandon Mahal, from the Departments of Radiation Oncology and Population Sciences at Dana-Farber Cancer Center in Boston, who has studied treatments for prostate cancer but was not involved in the new trial.
"The frequency that they occur is still a low percentage of patients with prostate cancer -- less than 5%," he said. "But the reason it's important is because there's an enzyme called the PARP enzyme that is involved in DNA repair. If there's a mutation in a DNA repair gene, like a BRCA mutation, then those cells may be more responsive to drugs like PARP inhibitors that block that PARP enzyme." For instance, olaparib is a PARP inhibitor drug.
There are several other ongoing trials examining the effectiveness of PARP inhibitors, including olaparib, to treat metastatic castration-resistant prostate cancer, Mahal said. As for the new phase III trial that was presented at the conference in Barcelona, he called those results "exciting."
"These findings suggest that olaparib may be beneficial in the treatment of patients with metastatic hormone-resistant prostate cancer and a mutation in DNA repair genes -- especially BRCA or ATM mutations," Mahal said.
"So the question now would be, how much would this medication olaparib apply for patients with other mutations?" he said. "The evidence appears to be convincing for the BRCA1, BRCA2 and ATM mutations."