BACKGROUND: A causal treatment effect of complete mesocolic excision for right-sided colon cancer on the risk of recurrence has been shown, but it is still unclear whether this is caused solely by a risk reduction of local recurrence.

OBJECTIVE: To assess to what extent complete mesocolic excision attributes to the risk of local recurrence.

DESIGN: Post-hoc analyses of data from a population-based cohort. Inverse probability of treatment weighting and competing risk analyses were used to estimate the possible causal effects of complete mesocolic excision.

SETTING: Data from the four public colorectal cancer centers in the Capital Region of Denmark.

PATIENTS: Patients undergoing elective colon resections for right-sided colon cancer without distant metastases during the period 2010-2013. One center performed complete mesocolic excision, the remainder conventional resections.

MAIN OUTCOME MEASURES: The primary outcome was the cumulative incidence of solely local recurrence 5.2 years after surgery. Secondary outcomes were solely distant recurrence and both local and distant recurrence diagnosed within 180 days.

RESULTS: A total of 807 patients were included with 186 undergoing complete mesocolic excision and 621 conventional resections. The 5.2-year cumulative incidence of a solely local recurrence was 3.7% (95% CI: 0.5-6.1) after complete mesocolic excision compared with 7.0% (5.0-8.9) in the control group, and the absolute risk reduction of complete mesocolic excision was 3.7% (2.5-7.1; p=0.035). The absolute risk reduction on local and distant recurrence was 3.4% (1.3-5.6; p=0.0019) and on solely distant recurrence 3.1% (0.0-6.2; p=0.0516).

LIMITATIONS: The recurrence risk after conventional resection might under estimated by the use of inappropriate modalities to diagnose local recurrence for some patients and the shorter duration in this group.

CONCLUSION: This study shows a causal treatment effect of complete mesocolic excision on the risk of a solely local recurrence and of distant recurrence with or without local recurrence. See Video Abstract at http://links.lww.com/DCR/B832 .