Supplementary Material for: Identification and validation of CCNA2 and CCNE2 as potential biomarkers in small cell lung cancer

Introduction: Small cell lung cancer (SCLC) is a special type of lung cancer sensitive to radiotherapy and chemotherapy but is prone to drug resistance and recurrence and has a very poor prognosis. This study aimed to explore the potential biomarkers and therapeutic targets for SCLC. Methods: After batch normalization of GSE40275, GSE1037, and GSE44447 datasets, R was used to screen SCLC's differentially expressed genes (DEGs) and hub genes. We use immunohistochemistry(IHC) to assess the tissue's expression level of the hub gene. The clinical value of the hub gene was further evaluated based on the collected clinical-pathological data. Results: In this study, a total of 230 DEGs (133 up-regulated and 97 down-regulated) were screened by the R package. The IHC showed that the expression of CCNA2 and CCNE2 in SCLC tissues was significantly higher than that in normal tissues (P<0.01). Overexpression of CCNA2 was closely associated with the extensive period of NCCN(P=0.004), tumor position (P=0.046), and clinical stage (P=0.002). The high expression levels of CCNE2 were related to high survival in chemotherapy patients (P=0.019). Conclusion: CCNA2 and CCNE2 may serve as potential biomarkers of diagnosis and treatment for SCLC.