Yeeun Shim

Investigation of PARP Inhibitor Resistance Based on Serially Collected Circulating Tumor DNA in Patients With BRCA -Mutated Ovarian Cancer

Abstract Purpose: Patient-specific molecular alterations leading to PARP inhibitor (PARPi) resistance are relatively unexplored. In this study, we analyzed serially collected circulating tumor DNA (ctDNA) from patients with BRCA1/2 mutations who received PARPis to investigate the resistance mechanisms and their significance in postprogression treatment response and survival. Experimental Design: Patients were prospectively enrolled between January 2018 and December 2021 (NCT05458973). Whole-blood samples were obtained before PARPi administration and serially every 3 months until progression. ctDNA was extracted from the samples and sequenced with a 531-gene panel; gene sets for each resistance mechanism were curated. Results: Fifty-four patients were included in this analysis. Mutation profiles of genes in pre-PARPi samples indicating a high tumor mutational burden and alterations in genes associated with replication fork stabilization and drug efflux were associated with poor progression-free survival on PARPis. BRCA hypomorphism and reversion were found in 1 and 3 patients, respectively. Among 29 patients with matched samples, mutational heterogeneity increased postprogression on PARPis, showing at least one postspecific mutation in 89.7% of the patients. These mutations indicate non-exclusive acquired resistance mechanisms—homologous recombination repair restoration (28%), replication fork stability (34%), upregulated survival pathway (41%), target loss (10%), and drug efflux (3%). We observed poor progression-free survival with subsequent chemotherapy in patients with homologous recombination repair restoration (P = 0.003) and those with the simultaneous involvement of two or more resistance mechanisms (P = 0.040). Conclusions: Analysis of serial ctDNAs highlighted multiple acquired resistance mechanisms, providing valuable insights for improving postprogression treatment and survival.

Circulating Tumor DNA and BRCA Reversion Mutation in Advanced or Recurrent Ovarian Cancer Patients With Germline Mutation.

Increasing number of ovarian cancer patients are receiving PARP inhibitor as maintenance or salvage therapy. Predictive factors to PARP inhibitor other than BRCA mutation or HRD status as well as specific resistance mechanism are unknown. Thus, the objective of this study was to prospectively collect serial blood samples in ovarian cancer patients with germline BRCA mutation who receive PARP inhibitor. We investigated circulating tumor DNA (ctDNA) before patients are started on PARP inhibitor and every 3 months thereafter until progression on PARP inhibitor. Through assessment of the changes in ctDNA mutational landscape, we aimed to investigate resistance mechanism to PARP inhibitor including BRCA reversion mutation.