240P - Unravelling the biological characteristics of MammaPrint extreme risk subgroups

MammaPrint® (MP) is a 70-gene based prognostic assay that stratifies early-stage breast cancer patients into low and high-risk of relapse. Recently, further stratification of the 70-gene risk results identified extreme low and high-risk subgroups with specific clinical outcomes (Delahaye et al. 2017) and treatment response characteristics (Wolf et al. 2017). However, the biological profiles of these extreme MP subgroups are not fully investigated. In this study, we aim to gain more insight into their biological significance using differentially expression genes (DEGs) analysis. We selected 400 samples from the whole MP range and defined 4 subgroups (Ultra high [UH], High risk [HR], Low risk [LR], Ultra low [UL]), for which FFPE microarray full-transcriptome data were available at Agendia. DEGs analysis was performed with limma and subsequent pathway analysis with Enrichr and GOrilla. Two separate comparative analyses were carried out to unravel biological processes associated with extreme risk subgroups: UL vs. LR and UH vs. HR. We found 101 DEGs (logFC>=0.485 & FDR