EGFR and non-small cell lung carcinoma: In NSCLC for example, these activating mutations are often located within exons 18–21, because this is the region of the EGFR gene that encodes the intracellular tyrosine kinase domain of the receptor.26 Depending upon the agent, EGFR-TKIs reversibly or irreversibly inhibit the binding of ATP within the tyrosine kinase domain and blunt receptor signaling.