Characterization of long-term responders following treatment with talazoparib (TALA) or physician's choice of chemotherapy (PCT) in the phase 3 embraca trial.

1029 Background: In the EMBRACA trial (NCT01945775), the poly(ADP-ribose) polymerase inhibitor (PARPi) TALA significantly improved progression-free survival (PFS) versus PCT in patients (pts) with germline BRCA1/2-mutated HER2-negative locally advanced/metastatic breast cancer (BC) (8.6 vs 5.6 months [mo]; hazard ratio [HR, 95% CI] 0.54 [0.41-0.71]; P < 0.0001). Predictive markers for response to PARPi, other than germline BRCA1/2 mutational status, are largely unknown. A previous analysis investigated biomarkers associated with long and short responders in EMBRACA. Here, we report the clinical characteristics of long and short responders. Methods: Pts were randomized 2:1 to TALA or PCT. In this retrospective analysis, pts in the intent-to-treat (ITT) population were mapped into two groups based on response: LONG (pts in TALA arm with overall survival [OS] ≥30 mo and duration of treatment ≥24 mo; pts in PCT arm with OS ≥30 mo); SHORT (pts in either arm with a PFS event [progressive disease by Independent Radiological Facility or death] ≤12 wks). Data cutoff date was Sept 30, 2019. Results: Of 431 pts randomized, 412 pts were treated (286 received TALA; 126 received PCT). In the ITT population, 37 pts receiving TALA and 34 pts receiving PCT were identified as LONG responders; 40 pts receiving TALA and 32 pts receiving PCT were SHORT responders. The Table shows a summary of pt characteristics for LONG and SHORT responders. More pts with HR+ BC and no prior CT for ABC were associated with LONG response; more pts with TNBC and ≥2 prior CT regimens or platinum were associated with SHORT response (Table). Median treatment duration for LONG responders (n = 37, TALA; n = 31, PCT) was 33.5 (24.0-61.4) mo for TALA and 7.6 (1.1-36.3) mo for PCT; 51.4% receiving TALA and 91.2% receiving PCT had subsequent therapy. In SHORT responders, median treatment duration was 2.0 (0.1-5.5) mo (TALA) and 1.4 (0.2-5.6) mo (PCT); 67.5% and 68.8% received subsequent therapy following TALA or PCT, respectively. Conclusions: In this clinical characterization of responders from the EMBRACA study, a higher number of LONG responders had HR+ BC and received no prior CT for ABC. A greater proportion of SHORT responders had TNBC and received ≥2 prior CT regimens or platinum. Further investigation is warranted in a larger number of pts. Clinical trial information: NCT01945775 .[Table: see text]