SCLC transformation has been identified as a resistance mechanism in 4%–14% of cases of EGFR-TKIs relapsed ADC.[14,63] Genomic sequencing of EGFR in transformed SCLC tumor samples revealed the preservation of the original EGFR-activating mutation, indicating that these transformed tumors were not de-novo cancers but rather a phenotypic change in response to treatment.[14] This suggested that the SCLC component becomes dominant after successful treatment with EGFR TKIs targeting the ADC component. The gene discussed is EGFR; the disease is small cell lung carcinoma.