PIK3CA and breast cancer: We used Gene Set Variation Analysis (GSVA) [30], an open-source enrichment analysis method, to calculate stemness and PI3K signaling scores on the basis of these gene expression signatures, independently in breast cancer tumors with available transcriptomic data from the METABRIC (n = 1980; used for primary analyses) and TCGA patient cohorts (n = 928; used for secondary analyses).