Examples of functional diversity and redundancy involving the EGFR-driven signaling system. A. Cross-communication between “dominant” and secondary” RTK signaling pathways and their alternating activation. Details are offered in . B. An example of alternate signaling pathways downstream of EGFR and leading to glioblastoma progression. In both pathways a central protein (aPKC) is the key signaling component, but the resulting complexes are formed in a different fashion and alternative oncogenic signals are relayed, which eventually converge to a common outcome: tumor progression (diagram adapted from Kusne et al., ).