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EP1230 Development of a pragmatic assay to assess homologous recombination competency in endometrial cancer
  1. CJH Kramer1,
  2. LM van Wijk2,
  3. MM de Jonge1,
  4. V Serra3,
  5. A Llop-Guevara3,
  6. CD de Kroon4,
  7. MPG Vreeswijk2 and
  8. T Bosse1
  1. 1Department of Pathology
  2. 2Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
  3. 3Experimental Therapeutics Group, Vall d’Hebron University Hospital, Vall d’Hebron Institute of Oncology (VHIO), Barcelona, Spain
  4. 4Department of Gynecology, Leiden University Medical Center, Leiden, The Netherlands


Introduction/Background Homologous recombination deficiency (HRD) is frequent in non-endometrioid endometrial cancer (EC), justifying clinical trials testing PARP-inhibitors. To facilitate this development a pragmatic test to asses HR competency is required. Accumulation of RAD51 protein at sites of DNA double strand breaks, has been put forward as a reliable functional test for HR competency. Here we aimed to test the performance of this pragmatic assay on formalin-fixed paraffin-embedded (FFPE) tumour tissue.

Methodology We used a previously described, prospective collected series of 21 EC that underwent primary resection with known HR status based on genomic analyses (next-generation sequencing for HR-core genes and array comparative genomic hybridization/SNP array) as our training cohort. To assure the presence of endogenous DNA damage, a gamma-H2AX staining was performed. Co-immunofluorescence (IF) was performed for both Geminin (marker staining cells in G2/S phase) and RAD51. RAD51 score was calculated as the fraction of Geminin positive cells that showed RAD51 foci (≥ 2) in the nucleus. Final RAD51 scores were correlated to known HR-status.

Results All 21 EC showed positivity for gamma-H2AX staining assuring presence of endogenous DNA damage in routine diagnostic FFPE tumour tissue. Among all cases, the RAD51scores varied form 0–72%. The range of RAD51 scores in the five HRD EC was 0–4%, whereas the 16 HRP EC tested showed RAD51 scores ranging from 16–72% (P<0.001).

Conclusion This RAD51 assay can successfully be performed on diagnostic FFPE material and reliably determined HR competency in 100% of our EC cases using cut-off RAD51 score of 10%. We will present the performance of this cut-off on our test-set of HR-annotated EC. This RAD51 assay is a promising cheap, pragmatic assay that can be used in the clinic to select patients that may benefit from platinum compounds and PARP-inhibitor therapy.

Disclosure Nothing to disclose.

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