Olaparib efficacy in patients with metastatic castration-resistant prostate cancer (mCRPC) carrying circulating tumor (ct) DNA alterations in BRCA1, BRCA2 or ATM: Results from the PROfound study.

Abstract

27 Background: ctDNA testing offers additional opportunities for homologous recombination repair (HRR) gene alteration determination in patients who are not able to access tumor tissue testing. Alteration testing in ctDNA, for BRCA1, BRCA2 and ATM alterations was performed retrospectively in the PROfound study (phase 3 trial of olaparib versus physician’s choice of abiraterone or enzalutamide in men with HRR gene-mutated mCRPC [NCT02987543]). Methods: ctDNA samples were sequenced at FMI, using the FoundationOne Liquid CDx assay for alterations in BRCA1, BRCA2 (BRCA) and ATM, using plasma samples collected during screening in PROfound. Only patients who consented and provided plasma samples from Cohort A (BRCA/ ATM alteration positive by tissue testing) were tested for ctDNA alterations. Radiographic progression-free survival (rPFS) assessed by blinded independent central review (BICR) in patients positive for alterations in ctDNA was analysed via stratified log-rank test. Additional efficacy endpoints (Objective Response Rate [ORR], Overall Survival[OS]) were also assessed. Results: In total, 181/245 (73.9%) Cohort A patients consented and provided a plasma sample for ctDNA testing, of which 139/181 (76.8%) had a ctDNA result reported (either mutation positive or mutation negative) and 42 patient samples failed testing due to insufficient DNA yield or a technical failure of the test.BRCA/ ATM alterations were identified in111/139 (79.9%) patients and 28/139 patients did not report a BRCA/ATM mutation either due to lack of ctDNA shedding from the tumour or ctDNA levels below the sensitivity of the assay. Patients who carried BRCA/ ATM ctDNA alterations had comparable demography, baseline characteristics and proportions of BRCA1, BRCA2 and ATM mutated patients to the overall Cohort A patients. rPFS by BICR results, in patients with BRCA/ ATM alterations in ctDNA, are presented in the Table. Key secondary efficacy endpoints (ORR, OS) will also be reported for ctDNA alteration positive patients. Conclusions: ctDNA testing in patients with mCRPC is feasible and most, but not all patients have concordant results. Patients who were positive for alterations in BRCA1, BRCA2 or ATM showed a consistent rPFS improvement (hazard ratio [HR] 0.33 [0.21, 0.53]) when compared with the ITT population identified by tumor tissue testing (HR 0.34 [0.25, 0.47]). This suggests that using ctDNA to identify patients carrying BRCA1, BRCA2 or ATM alterations who will benefit from olaparib may be beneficial. Clinical trial information: NCT02987543. [Table: see text]