Background: Small cell lung cancer (SCLC) is an aggressive and deadly neuroendocrine tumor derived from bronchial epithelial cells. Although it results in a 95% mortality rate, the development of targeted therapies for SCLCs has lagged behind. The aim of this study is to better research mutation characteristics of SCLC and identify potential biomarkers for target therapy.
Methods: We utilized high- resolution melting analysis to identify the mutations in epidermal growth factor receptor (EGFR ), Kirsten rat sarcoma viral oncogene (KRAS ), v-raf murine sarcoma viral oncogene homolog B1 (BRAF ), phosphatase and tensin homolog (PTEN ), and phosphatidylinositol-3-kinase catalytic (PIK3CA ) from the blood. A cohort of 99 SCLC patients including 44 limited-stage disease patients and 55 extensive-stage disease patients were prospectively collected. 
Results: EGFR  18 (G719X) mutation was found in 5 patients, EGFR  19 (del) mutation in 2, EGFR  20 (T790M) in 3, EGFR  21 (L858R) in 2, KRAS  2 (G13D) in 5, BRAF  15 (V600E) in 1, PIK3CA  9 (E542K) in 1, and no mutations in PTEN  5 (R130G), PTEN  6 (R173C), PTEN  8 (T319fs*1), and PIK3CA  20 (H1047R) were identified. Among these patients, two harbored EGFR  double mutation, one patient with EGFR  double mutation and KRAS  2 (G13D) mutation. 
Conclusion: The mutation form of EGFR  may differ from lung adenocarcinoma, and mutations of KRAS , BRAF , and PIK3CA  were rare in SCLC. These results aided us in comprehensively analyzing genetic features and laid the foundation for exploring the possibility of target therapy.
Keywords: epidermal growth factor receptor, small cell lung cancer, plasma, high-resolution melting