Background: Colonic stent is recommended as a bridge to elective surgery for malignant obstruction to improve short-term clinical outcomes for patients with colorectal cancer. However, since the oncological outcomes remain controversial, this study aimed to investigate the impact of self-expandable metallic stent (SEMS) on the tumor microenvironment. Methods: Patients treated with colonic stent as a bridge to surgery from 2010 to 2015 were identified from hospital records. Tumor biopsies and resected tumor samples of the eligible patients were retrieved retrospectively. Gene expression analysis was performed using the NanoString nCounter PanCancer IO 360 gene expression panel. Results: Of the 164 patients identified, this study included 21 who underwent colonic stent placement as a bridge to elective surgery. Gene expression analysis revealed 82 differentially expressed genes between pre- and post-intervention specimens, of which 72 were upregulated and 10 downregulated. Among the significantly upregulated genes, 46 are known to have protumor functions, of which 26 are specifically known to induce tumorigenic mechanisms such as proliferation, migration, invasion, angiogenesis, and inflammation. In addition, ten differentially expressed genes were identified that are known to promote antitumor functions. Conclusion: SEMS induces gene expressional changes in the tumor microenvironment that are associated with tumor progression in colorectal cancer and may potentiate a more aggressive phenotype. Future studies are warranted to establish optimal timing of surgery after SEMS insertion in patients with obstructive colorectal cancer.