Diverse BRCA1 and BRCA2 Reversion Mutations in Circulating Cell-Free DNA of Therapy-Resistant Breast or Ovarian Cancer

Purpose: Resistance to platinum-based chemotherapy or PARP inhibition in germline BRCA1 or BRCA2 mutation carriers may occur through somatic reversion mutations or intragenic deletions that restore BRCA1 or BRCA2 function. We assessed whether BRCA1/2 reversion mutations could be identified in circulating cell-free DNA (cfDNA) of ovarian or breast cancer patients previously treated with platinum and/or PARP inhibitors. <p>Experimental Design: cfDNA from 24 prospectively accrued BRCA1- or BRCA2-germline mutant patients, including 19 platinum-resistant/refractory ovarian cancer and five platinum and/or PARP inhibitor pre-treated metastatic breast cancer patients, was subjected to massively parallel sequencing targeting all exons of 141 genes and all exons and introns of BRCA1 and BRCA2. Functional studies were performed to assess the impact of the putative BRCA1/2 reversion mutations on BRCA1/2 function.</p> <p>Results: Diverse and often polyclonal putative BRCA1 or BRCA2 reversion mutations were identified in cfDNA from four ovarian cancer patients (21%) and from two breast cancer patients (40%). BRCA2 reversion mutations were detected in cfDNA prior to PARP inhibitor treatment in a breast cancer patient 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.</p> <p>Conclusions: Putative BRCA1/2 reversion mutations can be detected by cfDNA sequencing analysis in ovarian and breast cancer patients. Our findings warrant further investigation of cfDNA sequencing to identify putative BRCA1/2 reversion mutations and to aid the selection of patients for PARP inhibition therapy.

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