Unraveling the complexity of HRD assessment in ovarian cancer by combining genomic and functional approaches: translational analyses of MITO16-MaNGO-OV-2 trial

Background: Ovarian cancer (OvC) constitutes significant management challenges primarily due to its late-stage diagnosis and the development of resistance to chemotherapy. The standard treatment regimen typically includes carboplatin and paclitaxel, with the addition of poly (ADP-ribose) polymerase inhibitors for patients with high-grade serous ovarian cancer (HGSOC) harboring BRCA1/2 mutations. However, the variability in treatment responses suggests the need to investigate factors beyond BRCA1/2 mutations, such as DNA repair mechanisms and epigenetic alterations. Notably, homologous recombination repair deficiency (HRD) is observed in an additional 20% of HGSOC cases, indicating a broader spectrum of DNA repair defects. Existing commercial HRD assays have certain limitations, prompting a global effort to develop new genomic and functional tests through academic research. Materials and methods: This study investigates, in the 187 high-grade serous and endometrioid tumors from the MITO16/MaNGO-OV-2 trial, academic HRD genomic tests in conjunction with a RAD51 immunofluorescence assay to assess functional activation of HRD. Additionally, the study incorporates analysis of microRNA-506 (miR-506) expression as a putative epigenetic effector. Results: The RAD51 test identified HRD in 73% of the samples and genomic HRD testing in 57%, with HRD identified in 45% of samples by both tests. The significant discrepancy between the two assays emphasizes the need to refine tumor classification for HRD. A three-group genomic classification unveiled superior progression-free survival (PFS) in high- and mild-HRD tumors compared with negative-HRD tumors. High concordance between RAD51 and genomic testing in high-HRD tumors suggests a subset of 'super-HRD' tumors exhibiting superior PFS. High expression of miR-506 may be used to further refine HRD status. Conclusions: The study underscores the complexities of HRD assessment and advocates for a combined genomic and functional approach to enhance predictive accuracy in OvC treatment responses.