Risk of local recurrence of rectal cancer and circumferential resection margin: population-based cohort study

Background: A circumferential resection margin (CRM) of 1.0 mm or less after rectal cancer surgery is thought to increase the risk of local recurrence (LR). This retrospective population-based study examined how CRM distance affects the LR risk. Methods: Data from the Swedish Colorectal Cancer Registry were used in a retrospective analysis of rectal cancers resected between 2005 and 2013. The primary endpoint was LR. Results: A total of 12 146 patients were identified, of whom 8392 were included in the analysis; 739 patients had a CRM of 1.0 mm or less and 7653 had a CRM larger than 1.0 mm. The mean follow-up time was 51 months. There were 66 LRs (8.9 per cent) in the group with a CRM of 1.0mm or less, and 256 (3.3 per cent) among patients with a CRM larger than 1.0 mm. The LR rate was 17.0 per cent (27 of 159), 6.7 per cent (39 of 580), 1.9 per cent (2 of 103) and 3.4 per cent (254 of 7550) when the CRM was 0, 0.1-1.0, 1.1-1.9 and at least 2.0 mm respectively. The risk of LR among patients with a CRM of 0 mm was higher than that in all other subgroups with a larger CRM (P < 0.050). There was no difference in LR between the subgroups with CRM 1.1- 1.9 mm and at least 2.0 mm. LR was diagnosed earlier when the CRM was 1.0 mm or less. Conclusion: LR risk is related to exact CRM, with the highest risk in patients with a CRM of 0 mm. Close monitoring of patients with no measurable clear margin may allow early detection of LR.