EGFR and small cell lung carcinoma: Using both experimental systems and patient samples, secondary/gatekeeper mutations in EGFR (T790M), c-Met amplifications, PI3K mutations, and the acquisition of mesenchymal and small-cell lung cancer features have been identified and validated as molecular determinants of EGFR TKi resistance (Bell et al., 2005; Engelman et al., 2006; Shaw et al., 2009; Yao et al., 2010; Shaw and Engelman, 2016).