Abstract:Objective To investigate the mechanism, predictive factors, treatment and prognosis of transformation from non-small cell lung cacer to small cell lung cancer (SCLC). Methods A case of SCLC transformed from advanced lung adenocarcinoma after treatment with epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) was reported, and the diagnosis and treatment process were summarized and analyzed with a review of the literature. Results A 54-year-old male patient was admitted to hospital because brain metastasis of left lung adenocarcinoma was for more than 2 years and 7 months, and brain metastasis progressed for 3 months. Pathology showed SCLC after gamma knife treatment and lung biopsy for the patient. Etoposide and cisplatin(EP) chemotherapy was conducted for 4 cycles, and recombinant human endostatin injection combined with paclitaxel was given for one course of treatment when the disease progressed again. The patient′s condition is currently stable. Conclusion The inactivation of inhibitors RB1 and p53, long-term exposure to tyrosine kinase inhibitor (TKI), late-stage disease and higher serum NSE level are the important predictors for SCLC transformed from advanced lung adenocarcinoma after EGFR-TKI treatment. For lung adenocarcinoma patients with EGFR mutation, platinum etoposide chemotherapy should be considered as the first-line regimen when there is transformation to SCLC after EGFR-TKI treatment. 