Histological transformation of adenocarcinoma to small cell carcinoma lung as a rare mechanism of resistance to epidermal growth factor receptor-tyrosine kinase inhibitors: Report of a case with review of literature

A subset of non-small cell lung carcinoma (NSCC) harbor active mutations of epidermal growth factor receptor (EGFR). In these, EGFR tyrosine kinase inhibitors (EGFR-TKIs) are recommended as the first-line treatment. Though drug resistance is inevitable, histological transformation to small cell lung carcinoma (SCLC) is a rare mechanism for acquired resistance. Here we report one such rare case of histological transformation of pulmonary adenocarcinoma to small cell lung carcinoma in 46 year old male treated with Gefitinib.