Figure 2.

Physiological response to the activation of membrane receptors and immune receptors. Activation of receptor kinases, such as EGFR, FGFR, or HER-2, promotes the activation of RAS and its downstream pathways that facilitate cell growth, proliferation, cell survival, and differentiation. However, mutations in the RAS family lead to its constitutive activation and the hyperactivation of the downstream pathways—leading to uncontrolled cell survival. On the other hand, PD-L1 is present on the cell surface of immune cells and its binding to tumor cells PD-1 inhibits cell proliferation, cytokine secretion, and the expression of anti-apoptotic molecules in immune cells culminating in the escape of cancer from immunosurveillance. The goal of target therapies is to diminish the activation of abnormal signalling pathways, which can be inhibited at every step.