EGFR and small cell lung carcinoma: The mechanisms of acquired resistance to EGFR-TKIs involve the second-site mutations of EGFR (such as T790M gatekeeper mutation), activation of the bypass signaling pathways, epithelial-mesenchymal transition (EMT), the transformation of NSCLC to small cell lung cancer tissue, etc. (Westover et al., 2018; Wu and Shih, 2018).