57 Evolutions in rectal cancer MRI staging and risk stratification in the Netherlands 4 Risk classification All patients in the cohort were classified as low versus high risk, based on the original staging reports and based on the re-evaluations performed at the PI center, respectively, using the criteria detailed in Table 1. For the original staging reports, patients were classified as high risk in case of the presence of either of the following: ≥cT3 stage, cN1-2 stage, tumor-MRF distance of ≤1 mm; in line with clinical guidelines that applied during the main part of the study inclusion period (1-5,21). For the re-evaluation reports performed at the PI center, patients were classified as high-risk in case of ≥cT3cd stage, cN1-2 stage, tumor-MRF distance of ≤1 mm and/or presence of extramural vascular invasion (EMVI); in line with current guideline updates (3,14). Table 1 Criteria used for risk classification Original reports (“old” guidelines) Re-evaluation (“updated” guidelines) Low risk cT1-2 cN0 Tumour-MRF distance > 1 mm cT1-2-3ab cN0 Tumour MRF distance > 1 mm High risk cT3-4 cN1-2 Tumour-MRF distance ≤ 1 mm - cT3cd-4 cN1-2 Tumour-MRF distance ≤ 1 mm EMVI+ cT3a = < 1 mm invasion beyond rectal wall cT3b = 1-5 mm invasion beyond rectal wall cT3c = 5-15 mm invasion beyond rectal wall cT3d = > 15 mm invasion beyond rectal wall Statistical analyses Statistical analyses were performed using IBM SPSS Statistics version 25.0 (IBM Corporation, Armonk, NY, USA). Data was primarily analyzed using descriptive statistics where categorical or dichotomous variables were recorded as absolute numbers with percentages. Trends in completeness of reporting over time were analyzed by dividing the cohort into 3 equal time periods of ± 26 months (12/2011 to 2/2014; 3/2014 to 3/2016; 4/2016 to 6/2018). For intergroup comparison of categorical and dichotomous outcomes, the Pearson Chi-Square test was used. p values <0.05 were considered statistically significant. Results Patient cohort From the initial cohort of 1426, n=712 patient cases could be included (63.6% male, median age 66, range 26-94 years), for whom both the original primary staging reports
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