PIK3CA and breast cancer: PIK3CA mutant ER+ breast cancers exhibit an RNA expression profile of enhanced Wnt/β-catenin signaling, including up-regulation of Wnt target genes (AXIN2, LEF1, MYCN) and other components such as transcriptional regulators (TCF7L1, TCF7L2, CTNNB1), receptors (FZD4, FZD7) and ligands (WNT5A).