Discovery and validation of a transcriptional signature identifying homologous recombination-deficient breast, endometrial and ovarian cancers

Background Molecular alterations leading to homologous recombination deficiency (HRD) are heterogeneous. We aimed to identify a transcriptional profile shared by endometrial (UCEC), breast (BRCA) and ovarian (OV) cancers with HRD. Methods Genes differentially expressed with HRD genomic score (continuous gHRD score) in UCEC/BRCA/OV were identified using edgeR, and used to train a RNAseq score (ridge-regression model) predictive of the gHRD score (PanCanAtlas, N = 1684 samples). The RNAseq score was applied in independent gynaecological datasets (CARPEM/CPTAC/SCAN/TCGA, N = 4038 samples). Validations used ROC curves, linear regressions and Pearson correlations. Overall survival (OS) analyses used Kaplan-Meier curves and Cox models. Results In total, 656 genes were commonly up/downregulated with gHRD score in UCEC/BRCA/OV. Upregulated genes were enriched for nuclear/chromatin/DNA-repair processes, while downregulated genes for cytoskeleton (gene ontologies). The RNAseq score correlated with gHRD score in independent gynaecological cancers (R-2 = 0.4-0.7, Pearson correlation = 0.64-0.86, all P < 10(-11)), and was predictive of gHRD score >42 (RNAseq HRD profile; AUC = 0.95/0.92/0.78 in UCEC/BRCA/OV). RNAseq HRD profile was associated (i) with better OS in platinum-treated advanced TP53-mutated-UCEC (P < 0.001) and OV (P = 0.013), and (ii) with poorer OS (P < 0.001) and higher benefit of adjuvant chemotherapy in Stage I-III BRCA (interaction test, P < 0.001). Conclusions UCEC/BRCA/OV with HRD-associated genomic scars share a common transcriptional profile. RNAseq signatures might be relevant for identifying HRD-gynaecological cancers, for prognostication and for therapeutic decision.