Circumferential margin involvement after total mesorectal excision for mid or low rectal cancer: are all R1 resections equal?

Aim Our aim was to assess the prognostic influence of the circumferential resection margin ( CRM ) exact value after total mesorectal excision for mid or low rectal cancer. Methods All patients ( n  =   321) who underwent total mesorectal excision from 2005 to 2013 were identified from a prospective database, including 49 (15%) who presented with a CRM ≤ 1 mm. Four groups were defined: group 1, CRM  = 0 mm ( n  =   21); group 2, 0 <  CRM  ≤ 0.4 mm ( n  =   13); group 3, 0.4 <  CRM  ≤ 1 mm ( n  =   15); group 4, CRM  > 1 mm ( n  =   272). Results After a mean follow‐up of 42 ± 26 months, locoregional recurrence rates were 8/21 (38%) in group 1, 3/13 (23%) in group 2, 0/12 (0%) in group 3 and 26/272 (10%) in group 4 ( P  <   0.001), leading to significantly impaired 3‐year locoregional recurrence‐free survival in group 1 (57% ± 13%) and group 2 (56% ± 15%) compared to group 3 (85% ± 10%, vs group 1, P  =   0.021, vs group 2, P  =   0.049) and to group 4 (89% ± 2%, vs group 1, P  <   0.001, vs group 2, P  <   0.001). In multivariate Cox analysis, a CRM  ≤ 0.4 mm was identified as an independent factor impairing both locoregional recurrence‐free survival ( OR 3.14, 95% CI 1.53–6.46; P  =   0.002) and disease‐free survival ( OR 2.15, 95% CI 1.28–3.63; P  =   0.004). Conclusion Our study suggests that the prognosis after mid or low rectal cancer surgery was worse with a CRM  ≤ 0.4 mm. The prognosis was similar in patients with a CRM > 0.4 mm or ≤ 1 mm and patients with an R0 resection.