That’s the conclusion of investigators in the phase 2 BRCAAway trial, which compared a combination of abiraterone (Zytiga) and prednisone plus olaparib (Lynparza) against sequential therapy with the same agents.
At the time of data cutoff, median progression-free survival (PFS), the primary endpoint, was 39 months for patients randomized to the combination, compared with 8.4 months for those assigned to abiraterone/prednisone, and 14 months for those assigned to olaparib monotherapy, reported Maha Hussain, MD, of the Robert H. Lurie Comprehensive Cancer Center in Chicago.
“In patients with metastatic castration-resistant prostate cancer [mCRPC] and BRCA1/2 or ATM alterations, abiraterone and prednisone plus olaparib was well tolerated and resulted in better progression-free survival and response rates vs. single-agent olaparib or abiraterone/prednisone,” she said in an oral abstract presentation at the ASCO Genitourinary Cancers Symposium.
Although the study allowed crossover between the single-agent arms at the time of progression, only a few patients made the switch. Nonetheless, in these patients the PFS with the frontline combination was superior to that of sequential therapy, she noted.
Study Rationale and Design
Germline or somatic mutations in genes encoding for homologous recombination-repair occur in about 20% of men with mCRPC. Olaparib, a PARP1 (poly-adp ribose polymerase-1) inhibitor, interacts with androgen signaling, and preclinical studies have shown that castration-resistant prostate tumor cells have increased PARP1 activity. In addition, PARP1 has been shown preclinically to synergize with androgen receptor pathway inhibitors (ARPIs) such as abiraterone, Dr. Hussain explained.
The BRCAAway trial was designed to test whether co-targeting the androgen receptor and PARP1 could result in higher and more durable responses than current frontline therapies in patients with mCRPC with DNA-damage response mutations.
Patients with mCRPC with no prior exposure to either a PARP1 inhibitor, androgen receptor inhibitor, or mCRPC-directed chemotherapy underwent next-generation sequencing and germline testing of tumor tissues, and those patients found to have inactivating BRCA1/2 and/or ATM alterations were randomized on a 1:1:1 basis to either abiraterone 1000 mg daily plus prednisone 5 mg twice daily (19 patients); olaparib 300 mg twice daily (21 patients); or to the combination (21 patients).
The primary endpoint was radiographic PFS according to RECIST 1.1 criteria, Prostate Cancer Working Group 3 criteria, clinical assessment, or death.
As noted, the median PFS was 8.4 months with abiraterone/prednisone, 14 months with olaparib, and 39 months with the combination.
Secondary endpoints also favored the combination therapy arm, with objective response rates of 22%, 14%, and 33%, respectively; PSA response rates of 61%, 67% and 95%; and undetectable PSA response rates of 17%, 14%, and 33%.
A total of 8 of 19 patients on abiraterone were crossed over to olaparib, and 8 of 21 initially assigned to olaparib were crossed over to abiraterone. In these patients the median PFS from crossover was 8.3 and 7.2 months, respectively. In each crossover group the median PFS from the time of randomization was 16 months.
There were no grade 4 adverse events or treatment-related deaths reported in any of the study arms, and “essentially when you look at the adverse events, they pretty much are consistent with what you would expect to see with these particular agents,” Dr. Hussain said.
“Overall the patients were tolerating the treatment well,” she added.