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). This evidence concerns the gene LEF1 and breast cancer.