Transformation of epidermal growth factor receptor-mutated non-small cell lung cancer into small cell lung cancer—case report

Epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer (NSCLC) generally has a favorable prognosis when compared to lung cancer without this alteration due to the advent of EGFR tyrosine kinase inhibitors (TKI). However, during treatment with these drugs, acquired resistance and in turn progressive disease eventually occur. One such resistance mechanism is the transformation of EGFR-mutant adenocarcinoma into small cell lung cancer (SCLC) which has been described in a small subset of patients. We report the case of a woman with stage IV adenocarcinoma progressing and transforming into SCLC while being treated with Afatinib at our institution. This case also highlights the importance of rebiopsy in progressive patients receiving TKI for EGFR-mutated NSCLC.