Can covered self-expandable metal stents become a new standard in the treatment of obstructive colorectal cancer?—advantages, challenges, and future directions: a scoping review

Background: Self-expandable metal stent (SEMS) placement for obstructive colorectal cancer (OCC) is an established treatment option that helps avoid emergency surgery, improves short-term surgical outcomes, and increases primary anastomosis rates. However, recent meta-analyses suggest SEMS placement may increase recurrence following curative surgery, potentially due to mechanical and biomechanical stress on the tumor. Covered SEMS (CSEMS) were developed to suppress tumor ingrowth and reduce bowel injury, but evidence regarding their long-term efficacy and oncological safety remains insufficient. This review systematically analyzes the latest clinical and experimental evidence on CSEMS to clarify clinical utility, challenges, and future research priorities. Methods: We searched PubMed and Google Scholar for peer-reviewed English-language articles published between January 1994 and July 2025. Original studies and review articles related to CSEMS, including those involving OCC, were selected and narratively synthesized. We performed citation searching by screening reference lists and tracking citations of included studies and relevant reviews. We evaluated device variations and structural characteristics; technical and clinical success; complications; tumor ingrowth and overgrowth; surgical impact; macroscopic bowel effects; histopathological changes; biological effects; and long-term outcomes. Methodological limitations and knowledge gaps were explicitly assessed. Because heterogeneous study designs and outcomes precluded a high-quality meta-analysis, we adopted a scoping review approach. Studies reporting uncovered SEMS outcomes were also included for comparison. Results: Forty-eight studies were included. CSEMS showed high technical and clinical success rates, and the previously concerning risk of stent migration declined. Some studies suggested reduced deep venous invasion and bowel injury, but these benefits were not consistent across devices. CSEMS may attenuate bowel injury, and animal models showed no overt ischemia at anastomotic sites, suggesting a potential advantage over conventional SEMS in preserving anti-tumor immunity within the tumor microenvironment (TME). However, mechanical stress, mild hypoxia, and inflammatory responses cannot be completely avoided, and the extent and clinical significance of these effects—particularly regarding long-term oncologic outcomes—remain unclear. Conclusions: CSEMS could be a potential short-term bridge-to-surgery option, particularly for suppressing tumor progression and minimizing bowel injury. Unresolved issues include long-term oncological outcomes, stent migration management, tumor overgrowth, and the mechanisms underlying biological effects.