ERBB4 and breast cancer: Pathway analysis of the top 200 upregulated and 200 downregulated genes shows that systems known to be regulated by ErbB4 were altered in ErbB4−/− samples, such as RTK phosphorylation (cAMP, CREB, PKA, GPCRs); synaptogenesis and synaptic plasticity; and breast cancer and tumor microenvironment (Fig. 7c).