Survival after surgery beyond total mesorectal excision for primary locally advanced rectal cancer, a population-based study.

Background: The aim of this study was to compare relative survival in non-metastatic rectal cancer clinically staged as T3-T4 requiring beyond total mesorectal excision (TME) to that after standard TME.
Methods: This population-based study included all patients operated with anterior resection, abdominoperineal excision or Hartmann's procedure for non-metastatic rectal cancer clinically staged as T3-T4 in Sweden between 2009 and 2018. Relative survival was analysed in relation to surgery beyond TME (bTME), which was subcategorized as bTME- and bTME + to account for extent of resection. In all survival analyses, follow-up started at 90 days after surgery. Based on a causal model defined a priori excess mortality rate ratios (EMRR) were estimated using Poisson regression.
Results: Of 8272 included patients 1220 (14.7 %) were operated bTME. In a model adjusted for age and sex bTME was associated with higher excess mortality compared to standard TME (EMRR: 1.76, 95%CI:1.52-2.04). This association persisted after additional adjustment for tumour characteristics, neoadjuvant therapy and hospital volume (EMRR: 1.32, 95%CI:1.11-1.56) and was mainly attributable to restricted relative survival after bTME- (EMRR: 1.42, 95%CI:1.18-1.72) as EMRR after bTME+ was 1.07 (95%CI:0.80-1.44).
Conclusion: This national population-based study showed inferior relative survival after bTME compared to standard TME in non-metastasized rectal cancer cT3-cT4. Unexpectedly this difference was mainly seen after bTME of limited extent.
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