Circumferential resection margin as a prognostic factor after rectal cancer surgery: A large population-based retrospective study

Aim: This study aimed to investigate circumferential resection margin (CRM) as a prognostic factor for long-term oncologic survival after rectal cancer surgery. Methods: Patients diagnosed with malignant rectal cancer between 1 January 2010 and 31 December 2014, from the Surveillance, Epidemiology, and End Results (SEER) program were identified for this study. The patients were divided into five CRM groups to compare the baseline characteristics and assess cancer-specific survival (CSS): 0-1 mm, 1.1-2.0 mm, 2.1-5.0 mm, 5.1-10.0 mm, and >10 mm. The main endpoint was CSS. Results: Circumferential resection margin <= 1 mm was independently associated with 99% increased risk of cancer-specific mortality in rectal cancer [hazard ratio (HR) = 1.990, 95% confidence interval (CI) = 1.613-2.454, P < 0.001, using CRM (1.1-2.0 mm) as a reference]. CRM (5.1-10.0 mm) was independently associated with 29.2% decreased risk of cancer-specific mortality [HR = 0.708, 95% CI = 0.5250-0.954, P = 0.152, using group (2.1-5.0 mm) as reference]. CRM <= 2 mm or <= 0.4 mm was not obviously associated with CSS. Conclusions: circumferential resection margin is an independent prognostic factor in rectal cancer. Surgeons should try to maximize the CRM. Rectal cancer patients with CRM <= 1 mm should receive more postoperative attention depending on individual situation. Also, CRM should be accurately measured in millimeters in a preoperative magnetic resonance imaging or pathological report, rather than simply described as "involved" or "clear."