RAD51 as a biomarker for homologous recombination deficiency in high-grade serous ovarian carcinoma: robustness and interobserver variability of the RAD51 test

Abstract

Biomarker; High-hrade serous ovarian carcinoma; Homologous recombination deficiency

Biomarcador; Carcinoma de ovario seroso de alto grado; Deficiencia de recombinación homóloga

Biomarcador; Carcinoma d'ovari serós d'alt grau; Deficiència de recombinació homòloga

The RAD51 test is emerging as a promising biomarker for the assessment of functional homologous recombination deficiency (HRD). Yet, the robustness and reproducibility of the immunofluorescence-based RAD51 test, in different academic laboratories, have not been systematically investigated. Therefore, we tested the performance of the RAD51 assay in formalin-fixed paraffin-embedded (FFPE) high-grade serous ovarian carcinoma (HGSOC) samples in four European laboratories. Here, we confirm that subtle differences in staining procedures result in low variability of RAD51 and γH2AX scores. However, substantial variability in RAD51 scoring was observed in some samples, likely due to complicating technical and biological features, such as high RAD51 signal-to-noise ratio and RAD51 heterogeneity. These results support the need to identify and perform additional quality control steps and/or automating image analysis. Altogether, resolving technical issues should be a priority, as identifying tumours with functional HRD is urgently needed to guide the individual treatment of HGSOC patients. Follow-up studies are needed to define the key tissue quality requirements to assess HRD by RAD51 in FFPE tumour samples, as this test could help in guiding the individual treatment of HGSOC patients.

This work was supported by the Dutch Cancer Society (KWF) (grant: 12995 to TB and MV) and by ERA PerMed (grant ERAPERMED2019-215 to VS). VS received funding from Instituto de Salud Carlos III (CPII19/00033). ALG received funding from Asociación Española Contra el Cáncer (AECC) (INVES20095LLOP) and AHR from Generalitat de Catalunya (PERIS SLT017/20/000081).