SCLC transformation has been described as a resistance mechanism to EGFR directed TKIs in approximately 5% of patients and has been observed after both first-generation and subsequent third-generation EGFR TKIs.[1,2,5] The 2 cases in this study were initially diagnosed with lung adenocarcinoma harboring EGFR exon 19 mutation. This evidence concerns the gene EGFR and small cell lung carcinoma.