ATF3 and breast cancer: The canonical Wnt/β-catenin signaling pathway is upregulated and/or activated in ATF3-induced mammary tumors [10], which may affect tumor heterogeneity in BLBCs [30,31] and GSEA revealed that, in addition to enrichment of the canonical Wnt pathway, non-canonical Wnt pathways were also enriched in ATF3-induced mammary tumors (Figure 2Bb,Bc).