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• The genomic characteristics and mutations in Notch signaling pathway-related genes of SCLC patients were clarified. • The relationship of Notch signaling pathway mutations with tumor immune microenvironment were analyzed. • There was a significant negative correlation between NOTCH 1 gene mutation status and PD-L1 protein expression level. • Patients with positive DLL3 expression and no NOTCH 1 gene mutation had higher PD-L1 expression and may be more likely to benefit from PD-1/PD-L1 ICIs treatment. To explore the characteristics of Notch pathway in small cell lung cancer (SCLC), clarify the expression of delta-like protein 3 (DLL3) in SCLC patients undergoing surgical treatment, and explore the correlation between DLL3 expression and clinicopathological features, prognosis, and immune microenvironment. A total of 134 patients who received surgical treatment and were diagnosed as SCLC by postoperative histopathology were enrolled. All exon gene sequencing was performed in tumor tissues and adjacent normal tissues of 28 patients to clarify the genomic characteristics of SCLC. The expressions of DLL3 and programmed cell death 1 ligand 1 (PDL1) were detected by immunohistochemistry (IHC) in 101 postoperative pathological specimens. Notch receptor mutations are common, but the overall mutation rate of Notch ligand family is not high and mutually exclusive. The mutation status of Notch and Notch1 gene were not related to the prognosis. Notch1 gene mutation was significantly negatively correlated with the expression of PD-L1. DLL3 was highly expressed in SCLC and had no significant correlation with prognosis. There was a positive correlation between DLL3 expression and PD-L1 expression. Patients with positive DLL3 expression and no NOTCH 1 gene mutation had higher PD-L1 expression. SCLC patients with such characteristics may be more likely to benefit from immunotherapy. This study preliminarily explored the genomic characteristics and immune microenvironment of surgical resection of SCLC in China, and found the correlation between Notch gene mutation, DLL3 expression and PD-L1 expression, which provided a new idea for selecting appropriate treatment strategies for SCLC in the future. [ABSTRACT FROM AUTHOR]