Objective To explore whether blood exosome carrying miR-140-3p can regulate the malignant progression of small cell lung cancer (SCLC) through targeting ubiquitin-conjugating enzyme E2C (UBE2C). MethodsThis study was consisted of bioinformatics analysis, clinical research, cell analysis, and animal experiments. We searched GEO database for data of SCLC related microRNA (miRNA) dataset GSE19945, mRNA dataset GSE40275, and GSE60052. T-test was used to detect the differential expression of miR-140-3p in normal tissues and SCLC tissues in the dataset, and the expression of miR-140-3p in different tissues and extracellular vesicles was analyzed through a database. SCLC tissue and paired cancerous tissues excised at Yongzhou Central Hospital were collected between December 2021 and December 2022, and healthy volunteers 7 days before the start of the study was selected. Quantitative real-time polymerase chain reaction was used to detect the expression level distribution of miR-140-3p and UBE2C in tissue samples of SCLC patients and healthy volunteers. SCLC patients were divided into low expression and high expression groups based on the median expression level, and the correlation between the expression levels of miR-140-3p and UBE2C and patient pathological parameters was analyzed. 20 male nude mice was selected. The nude mice were randomly divided into 4 groups: miR-140-3p, UBE2C analog negative control group, and analog control group, with 5 mice in each group. Immunohistochemical detection system was used to detect tumor tissue sections in nude mice. Results A total of 45 patients and 30 healthy volunteers were included. SCLC malignant progression was significantly associated with the expression of miR-140-3p and UBE2C. The expression of miR-140-3p was low in blood-derived exosomes from SCLC patients. Overexpression of miR-140-3p inhibited the proliferation (47.33±2.52 vs. 107.67±10.69, P<0.05), migration [(11.63±2.62)% vs. (31.77±4.30)%, P<0.05] and invasion (44.33±3.06 vs. 102.67±8.50, P <0.05) and promoted their apoptosis [(14.48±1.20)% vs. (10.14±1.21)%, P<0.05]. Bioinformatics analysis yielded the target gene UBE2C of miR-140-3p. In vitro experiments further demonstrated that miR-140-3p directly targetd UBE2C to inhibit SCLC cell proliferation, migration, invasion, epithelial mesenchymal transition, and promote apoptosis. Mouse xenotransplantation experiments showed that miR-140-3p mimic significantly inhibited tumor growth. ConclusionTherefore, the miR-140-3p extracellular vesicle and the oncogenic gene UBE2C may be potential targets for inhibiting the malignant progression of SCLC.