ERBB2 and breast cancer: Figure 6 summarizes the cell proliferation pathways in breast cancer adapted from the KEGG database (https://www.genome.jp/kegg-bin/show_pathway?hsa0 5224+3845). As indicated in Figure 6, in luminal A, the signals are mainly transmited via the hormone receptors. However, the RAS/Raf/MEK signaling pathway is a key cell proliferation path in luminal B, HER2, and basal-like subtypes. This Figure 6 also shows that HER2 activity can enhance the RAS/Raf/MEK path signaling.