Conference Coverage

PARP inhibitor prolongs PFS in mCRPC


 

REPORTING FROM ESMO 2019

BARCELONA – PARP inhibitors may be able to do for men with advanced castration-resistant prostate cancer what they currently do for women with breast or ovarian cancers linked to BRCA mutations, investigators report.

Dr. Maha Hussain, Northwestern University, Chicago Neil Osterweil/MDedge News

Dr. Maha Hussain

Among men with metastatic castration-resistant prostate cancer (mCRPC) that had progressed on prior therapy with either abiraterone (Zytiga) or enzalutamide (Xtandi) and that bore DNA-repair mutations (BRCA1, BRCA2, or ATM), those who were randomized in the PROfound trial to receive olaparib (Lynparza) had significant improvement in radiographic progression-free survival (rPFS) compared with patients assigned to the physician’s choice of a new hormonal agent, reported Maha Hussain, MD, of the Robert H. Lurie Comprehensive Cancer Center at Northwestern University in Chicago.

“PROfound is the first positive biomarker-selected phase 3 study evaluating a molecularly-targeted therapy in men with metastatic castration-resistant prostate cancer, highlighting the importance of genomic testing in this population, and also importantly highlighting the feasibility of precision-medicine trials in this disease,” she said at the European Society for Medical Oncology (ESMO) Congress.

Approximately 25% of men with mCRPC have loss-of-function mutations or alterations in homologous recombinant repair (HRR) genes, especially BRCA1, BRCA2, and ATM. Breast and ovarian cancers bearing these mutations are known to be sensitive to PARP (poly ADP ribose polymerase) inhibitors such as olaparib.

To see whether men with mCRPC could derive a similar benefit, the investigators enrolled patients who had experienced disease progression on abiraterone or enzalutamiude and whose tumors had one or more alterations in any qualifying gene with direct or indirect role in homologous recombinant DNA repair.

Patients were stratified by previous taxane use and measurable disease, and then two cohorts were enrolled. Cohort A included 245 men with BRCA1, BRCA2, or ATM mutations, and cohort B included 142 men with other alterations (in BARD1, BIRP1, CDK12, CHEK1, CHEK2, FANCL, PALB2, PPP2R2A, RAD15B, RAD15C, RAD15D, or RAD54L).

The median age in cohort A was 68, and in cohort B it was 67, with men 86 years of age at the upper end of the range.

“I think it’s remarkable that men in their late 80s and even early 90s were eligible, were able to be enter this study and be treated on it, and I think that’s an important point here,” Dr. Hussain said.

Nearly one-fourth of patients in the trial had metastatic disease at their initial diagnosis, she noted.

Patients in each cohort were randomized on a 2:1 basis to receive either open-label olaparib 300 mg twice daily, or the treating physician’s choice of abireraterone or enzalutamide, plus predisone.

Upon blinded independent central review (BICR) showing disease progression, patients were allowed to cross over to the olaparib arm, which more than 80% of patients eventually did.

Radiographic PFS in the BRCA1, BRCA2 and ATM cohort according to BICR, the primary endpoint, was a median of 7.39 months with olaparib, compared with 3.55 months with the other therapies, for a hazard ratio (HR) for progression on olaparib of 0.34 (P less than .0001).

A somewhat smaller but still significant benefit was seen for olaparib in the overall population (both cohorts), with a median rPFS of 5.82 months vs. 3.52 months, respectively (HR 0.49, P less than .0001).

Among patients in cohort A, the objective response rate was 33.3% with olaparib, compared with 2.3% for the other agents, resulting in an odds ratio for response of 20.86 (P less than .0001)

Olaparib was also associated with longer time to pain progression in patients in cohort A, with the median not reached compared with 9.92 months with the hormonal agents (HR 0.44, P = .0192).

Among patients in the physician’s choice arm who had disease progression, 80.6% in cohort A and 84.6% in cohort B were crossed over to olaparib.

At this interim analysis, median overall survival was 18.5 months with olaparib, compared with 15.11 months with the other agents, but this difference was not statistically significant. Further follow-up will be needed before a difference in overall survival becomes evident, Dr. Hussain said.

“I think this study has demonstrated that now prostate cancer can be treated with a targeted therapy approach,” said Ignacio Duran, MD, of Hospital Universitario Marques de Valdecilla in Santander, Spain. He was the invited discussant and moderator of a briefing where Dr. Hussain outlined the study details prior to presentation in a symposium.

Dr. Ignacio Duran, Hospital Universitario Marques de Valdecilla in Santander, Spain Neil Osterweil/MDedge News

Dr. Ignacio Duran

“Not all prostate cancer patients have the same tumors, and this is the first time we’ve been able to identify that we can more precisely characterize the molecular biology, the genetic background of these tumors, and that is going to determine how we treat them,” he said.

The PROfound trial made “a double hit: superiority in terms of efficacy, and it has proved a new concept that in prostate cancer has not been proved before,” he added.

“This is a truly practice-changing study, not just for our practice and our patients, but also for the study design,” said Eleni Efstathiou, MD, PhD, of the University of Texas MD Anderson Cancer Center in Houston, who was the invited discussant at the symposium where Dr. Hussain presented the full trial data.

Dr. Eleni Efstathiou, University of Texas MD Anderson Cancer Center in Houston Neil Osterweil/MDedge News

Dr. Eleni Efstathiou

She lauded the use of a validated genomic testing tissue-based assay (FoundationOne CDx next-generation sequencing test) to identify patients who might benefit from olaparib.

She said that the PARP inhibition-specific strategy of the trial appears to have paid off, with statistically significant, clinically meaningful improvement in outcomes and an acceptable safety profile.

“And when it comes to a prostate cancer therapy strategry? Well, we’re starting to enter into the targeted therapy era,” she said.

The PROfound trial was sponsored by AstraZeneca and is part of an alliance between AstraZeneca and Merck. Dr. Hussain disclosed travel and/or accommodation support, honoraria, consulting/advisory fees and research support from AstraZeneca and others. Dr. Duran disclosed advisory board fees from Roche and BMS, and speaker honoraria from Roche, Bristol-Myers Squibb, and Merck. Dr. Efstathiou disclosed research support and honoraria from various companies, not including AstraZeneca or Merck.

SOURCE: Hussain M et al. ESMO 2019, Abstract LBA-12.

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