Fig. 2

Mechanisms of RTKs (EGFR) signal transduction, small molecule inhibition and monoclonal antibody inhibition in target therapy. This depicts EGFR and RTK signaling. The extracellular domain is Leucine-rich binding domain and cysteine-rich domains, the kinase domain is the ATP catalytic domain and the C-terminal domain is composed of tyrosine residues (Y). The Ras–Raf–MEK–MAPK pathway is activated through stimulation by growth factor receptor. The phosphatidylinositol 3-kinase (PI3K)– AKT and signal transducer and activator of transcription (STAT) proteins (STAT1, STAT3, and STAT5) are also activated. The synergistic effects of these pathways bring about proliferation, cell survival, cell motility, adhesion, and angiogenesis. Deregulation of the pathway causes activation of the downstream oncogenic signaling cascades. Small-molecule tyrosine kinase inhibitors block downstream signaling by competitively competing for the ATP at the catalytic site of the kinase domain while monoclonal antibodies (mAbs) with an outstanding degree of specificity block signaling by binding to the leucine-rich and cysteine-rich ectodomain (cetuximab in EGFR)