What is more, PIK3CA mutation, [12] ERBB2 amplification, [13] HGF overexpression, [14] AXL activation, [15] epithelial-mesenchymal transition, and pathology type transformation, especially adenocarcinoma transformation into small cell lung cancer, have also been reported as causes of secondary resistance to EGFR-TKIs. This evidence concerns the gene EGFR and adenocarcinoma.