EGFR and small cell lung carcinoma: On the contrary, acquired resistance occurs in patients who initially benefited from EGFR-targeted therapies and the underlying mechanisms of acquired resistance include EGFR T790M mutation, activation of bypass signaling (such as MET amplification, HER2 upregulation or KRAS activation), and histologic transformation to small cell lung cancer or epithelial-mesenchymal transition [7].