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Aim: To investigate the conflicting consequences of faecal diversion on stoma outcomes and anastomotic leakage in anterior resection for rectal cancer, including interaction effects determined by the extent of mesorectal excision.

Method: Anterior resections between 2007 and 2016 were identified using the Swedish Colorectal Cancer Registry. National Patient Registry data were added to determine stoma outcome 2 years after surgery. Tumour distance from the anal verge constituted a proxy for extent of mesorectal excision [total mesorectal excision (TME): ≤10 cm; partial mesorectal excision (PME): 13–15 cm]. With confounder-adjusted probit regression, the total effect of defunctioning stoma on permanent stoma, and the interaction effect of extent of mesorectal excision, were estimated together with the indirect effect through anastomotic leakage. Baseline risks, risk differences (RDs) and relative risks (RRs) were reported.

Results: The main study cohort included 4529 patients. Defunctioning stomas influenced the absolute permanent stoma risk (TME: RD 0.11 [95% CI 0.09–0.13]; PME: RD 0.15 [95% CI 0.13–0.16]). The baseline risk was higher in TME, with a resulting greater RR in PME (2.23 [95% CI 1.43–3.02] vs 4.36 [95% CI 3.05–5.68]). The indirect reduction in permanent stoma rates, due to the alleviating effect of faecal diversion on anastomotic leakage, was small (TME: 0.89 [95% CI 0.81–0.96]; PME: 0.96 [95% CI 0.91–1.00]).

Conclusion: In anterior resection for rectal cancer, defunctioning stomas may reduce chances of a stoma-free outcome. Considering leakage reduction benefits, consequences of routine diversion in TME might be fairly balanced, while this seems questionable in PME.