Recent studies have shown that the efficacy of PARP inhibitors in epithelial ovarian
carcinoma (EOC) is related to tumor-specific defects in homologous recombination (HR) and extends
beyond BRCA1/2 deficient EOC. A robust method with which to identify HR-deficient (HRD)
carcinomas is therefore of utmost clinical importance. In this study, we investigated the proficiency of
a functional HR assay based on the detection of RAD51 foci, the REcombination CAPacity (RECAP)
test, in identifying HRD tumors in a cohort of prospectively collected epithelial ovarian carcinomas
(EOCs). Of the 39 high-grade serous ovarian carcinomas (HGSOC), the RECAP test detected 26%
(10/39) to be HRD, whereas ovarian carcinomas of other histologic subtypes (n = 10) were all
HR-proficient (HRP). Of the HRD tumors that could be sequenced, 8/9 showed pathogenic BRCA1/2
variants or BRCA1 promoter hypermethylation, indicating that the RECAP test reliably identifies
HRD, including but not limited to tumors related to BRCA1/2 deficiency. Furthermore, we found a
trend towards better overall survival (OS) of HGSOC patients with RECAP-identified HRD tumors
compared to patients with HRP tumors. This study shows that the RECAP test is an attractive alternative to DNA-based HRD tests, and further development of a clinical grade RECAP test is
clearly warranted