A RAD51 Functional Assay As a Candidate Test for Homologous Recombination Deficiency in Ovarian Cancer.

Rationale. Homologous recombination deficiency (HRD), defined as BRCA1/2 mutation (BRCAmut) or high genomic instability, is used to identify ovarian cancer (OC) patients most likely to benefit from PARP inhibitors. While these tests are useful, they are imperfect. Another approach is to measure the capacity of tumor cells to form RAD51 foci in the presence of DNA damage using an immunofluorescence assay (IF). We aimed to describe for the first time this assay in OC and correlate it to platinum response and BRCAmut.Methods. Tumor samples were prospectively collected from the randomized CHIVA trial of neoadjuvant plat-inum +/- nintedanib. IF for RAD51, GMN and gH2AX was performed on FFPE blocks. Tumors were considered RAD51-low if <= 10% of GMN-positive tumor cells had >= 5 RAD51 foci. BRCAmut were identified by NGS.