Diverse and Reversion Mutations in Circulating Cell-Free DNA of Therapy-Resistant Breast or Ovarian Cancer.

Resistance to platinum-based chemotherapy or PARP inhibition in germline or mutation carriers may occur through somatic reversion mutations or intragenic deletions that restore BRCA1 or BRCA2 function. We assessed whether reversion mutations could be identified in circulating cell-free DNA (cfDNA) of patients with ovarian or breast cancer previously treated with platinum and/or PARP inhibitors. cfDNA from 24 prospectively accrued patients with germline or mutations, including 19 patients with platinum-resistant/refractory ovarian cancer and five patients with platinum and/or PARP inhibitor pretreated metastatic breast cancer, was subjected to massively parallel sequencing targeting all exons of 141 genes and all exons and introns of and Functional studies were performed to assess the impact of the putative reversion mutations on BRCA1/2 function. Diverse and often polyclonal putative or reversion mutations were identified in cfDNA from four patients with ovarian cancer (21%) and from two patients with breast cancer (40%). reversion mutations were detected in cfDNA prior to PARP inhibitor treatment in a patient with breast cancer who did not respond to treatment and were enriched in plasma samples after PARP inhibitor therapy. Foci formation and immunoprecipitation assays suggest that a subset of the putative reversion mutations restored BRCA1/2 function. Putative reversion mutations can be detected by cfDNA sequencing analysis in patients with ovarian and breast cancer. Our findings warrant further investigation of cfDNA sequencing to identify putative reversion mutations and to aid the selection of patients for PARP inhibition therapy. .