Analysis of real-world (RW) data for metastatic breast cancer (mBC) patients (pts) with somatic BRCA1/2 (sBRCA) or other homologous recombination (HR)-pathway gene mutations (muts) treated with PARP inhibitors (PARPi).

Abstract

10512 Background: PARPi are approved for treatment of pts w/ HER2-negative mBC and germline BRCA1/2 (g BRCA) pathogenic or likely pathogenic variants (muts); however, clinical benefit has also been demonstrated in mBC pts w/ sBRCA or other HR-pathway gene muts. Using a RW Clinico-Genomic Database (CGDB), we assessed outcomes for pts w/ gBRCA muts compared to pts w/ either s BRCA or other HR-pathway muts treated w/ PARPi. Methods: 6,329 mBC pts from ̃280 US cancer clinics were included in the Flatiron Health (FH) -Foundation Medicine (FM) CGDB, which includes comprehensive genomic profiling (CGP) linked to de-identified, electronic health record (EHR)-derived clinical data. Eligible pts had mBC, received care in the FH network from 1/1/2011-9/1/2020, and had tissue CGP by FM. Pts classified as gBRCA: positive germline result in EHR and BRCA mut predicted germline per FM’s somatic, germline, zygosity algorithm (SGZ) (Sun et al PMID 29415044). Non-g BRCA: negative germline results in EHR and a somatic BRCA (s BRCA) mut per SGZ or BRCA wild-type w/ another HR mut per CGP result. Pts w/o a documented gBRCA result in EHR, unknown FM BRCA SGZ result, or conflicting results were excluded. RW overall survival (rwOS) and RW progression-free survival (rwPFS) from start of PARPi for pts w/ gBRCA and non- gBRCA mBC were compared using Kaplan-Meier analysis and Cox regression adjusted for mBC line number, prior platinum, age at PARPi initiation, race, and receptor status. Results: Among pts who received PARPi in the mBC setting, 44 had gBRCA and 18 had non -gBRCA: 9 s BRCA (5 BRCA1, 4 BRCA2), 4 PALB2, 2 ATM, and 1 each of ATM+CDK12, BARD1+FANCF+RAD54L, and CHEK2. Of HR muts 76% were confirmed biallelic: 33/44 gBRCA (11 unknown), 8/9 sBRCA, 3/4 PALB2, and 3/5 other (1 unknown). Neither median rwPFS nor rwOS from start of PARPi were significantly different between the non-g BRCA and g BRCA cohorts (rwPFS: 7.0 [4.6-11.3] vs 5.5 [4.3-7.2] months (mos), aHR: 1.19 [0.57 – 2.43]; rwOS: 15.0 [7.95-16.3] vs 11.5 [9.46-NA] mos, aHR: 0.85 [0.36-1.98]). For 9 pts w/ sBRCA mut, median rwPFS was 7.1 mos (range 1.4-12.4) and all pts had progressed by data cut off. Conclusions: Despite small pt numbers and limitations from RW data, our results suggest that pts w/ biallelic non-g BRCA mBC may derive similar benefit from PARPi when tumor CGP detects a s BRCA mut or germline or somatic mut in other HR-pathway genes. These findings are consistent w/ the results from TBCRC-048 (Tung et al PMID 33119476) and support further randomized trials exploring the efficacy of PARPi in this population.[Table: see text]