PIK3CA and breast neoplasm: Likewise, integrative correlative studies between pathway-specific gene expression signature scores, gene level DNA segment scores and RNAi shRNA abundance led to the identification of 21 amplified, essential and putative driver oncogenes in highly proliferative luminal breast cancers as well as the identification of SOX4 as a driver of PI3K signaling in basal-like breast tumors [99,137].