OC04.06: A comparison of the homologous recombination deficiency test success rate using samples from ultrasound‐guided biopsies and those obtained during laparotomies in advanced ovarian cancer

Testing for tumour homologous recombination deficiency (HRD) is recommended for all patients with advanced high-grade epithelial ovarian cancer and directs first-line treatment in these patients. We set out to identify the factors that influence HRD test success and the average time-to-result. We hypothesised that samples taken during surgery would result in a higher test success rate than those obtained using ultrasound (US) guided biopsy. We also hypothesised that diagnostic biopsies taken with a larger needle gauge would result in greater rates of test success. This was a retrospective cohort review of 125 patients with advanced high-grade epithelial ovarian cancer tested for HRD. Tissue for HRD testing was collected either at primary surgery, or from US-guided diagnostic biopsy if patients had upfront chemotherapy. In case of test failure at diagnostic biopsy, further tissue was obtained during interval debulking surgery. 85.6% of patients received a result from their first test. Including repeated tests (due to test failure), a total of 148 HRD tests were performed. The overall success rate of HRD testing was 69.6%. Chances of obtaining a result was 66.7% (n = 40/60) from diagnostic biopsy, 91.5% (n = 42/47) from primary surgery, and 51.2% (n = 21/41) from interval debulking surgery. At US-guided biopsy, needle gauge significantly affected the test success rate. There was a 100% success rate with 16-gauge (n = 14/14) versus 64.5% with 18-gauge needles (n = 20/31). Of 148 tests carried out, 27% returned results in ≤ 21 days (median 28 days, range 14-158 days). 84.6% of patients with HRD-positive tumours treated at our centre received PARP-inhibitors as part of their first-line maintenance treatment. At US-guided biopsy, test failure rates were higher if samples were taken using an 18-gauge needle versus 16-gauge needle. By optimising HRD testing, we can optimise treatment at the earliest timepoint possible.