The Need for Consensus and Transparency in Assessing Population-Based Rates of Positive Circumferential Radial Margins in Rectal Cancer: Data from Consecutive Cases in a Large Region of Ontario, Canada

Background A positive circumferential radial margin (CRM) after rectal cancer surgery is an important predictor of local recurrence. The definition of a positive CRM differs internationally, and reported rates vary greatly in the literature. This study used time-series population-based data to assess positive CRM rates in a region over time and to inform future methods of CRM analysis in a defined geographic area. Methods Chart reviews provided relevant data from consecutive patients undergoing rectal cancer surgery between 2006 and 2012 in all hospitals of the authors’ region. Outcomes included rates for pathologic examination of CRM, CRM distance reporting, and positive CRM. The rate of positive CRM was calculated using various definitions. The variations included positive margin cutoffs of CRM at 1 mm or less versus 2 mm or less and inclusion or exclusion of cases without CRM assessment. Results In this study, 1222 consecutive rectal cancer cases were analyzed. The rate for pathology reporting of CRM distance increased from 54.7 to 93.2 % during the study. Depending on how the rate of positive CRM was defined, its value varied 8.5 to 19.4 % in 2006 and 6.0 to 12.5 % in 2012. Using a pre-specified definition, the rate of positive CRM decreased over time from 14.0 to 6.3 %. Conclusions A marked increase in CRM distance reporting was observed, whereas the rates of positive CRM dropped, suggesting improved pathologist and surgeon performance over time. Changing definitions greatly influenced the rates of positive CRM, indicating the need for more transparency when such population-based rates are reported in the literature.