The Derivation and External Validation of a Fibrosis Risk Model for Colorectal Tumours Undergoing Endoscopic Submucosal Dissection.

Background: Endoscopic submucosal dissection (ESD) is an advanced technique that can become more challenging in the presence of submucosal fibrosis. Predicting the grade of fibrosis is important in order to identify technically difficult ESD. Aims and Methods: Our study aimed to derive and validate a prediction model to determine the preoperative degree of submucosal fibrosis in colorectal tumours undergoing ESD. A predictive model was developed to derive the probability of an increasing submucosal fibrosis in the derivation cohort and then externally validated. Results: 309 patients (age: 68 ± 10.9 years) underwent colorectal ESD between January 2016 and June 2020. F0, F1, and F2 fibroses were reported in 196 (63.4%), 70 (22.6%), and 43 (13.9%) cases, respectively. R0 resection was found in 266 (87%) lesions. At multivariable analysis in the derivation cohort, lesion morphology (OR = 0.37 and CI = 0.14-0.97 for LST-NG vs. 0-Is; OR = 0.29 and CI = 0.1-0.87 for the LST mixed type vs. 0-Is; and OR = 0.32 and CI = 0.1-1.03 for LST-G vs. 0-Is) and increasing size (OR = 1.02 and CI = 1.01-1.04 for a 1 mm increase) were significantly associated with an increasing degree of fibrosis. The model had fair discriminating ability in the derivation group (AUROC = 0.61 and CI = 0.52-0.69 for F1-F2 vs. F0 fibroses; AUROC = 0.61 and CI = 0.45-0.77 for F2 vs. F0-F1 fibroses) and in the validation group (AUROC = 0.71 and CI = 0.59-0.83 for F1-F2 vs. F0 fibroses; AUROC = 0.65 and CI = 0.52-0.77 for F2 vs. F0-F1 fibroses). Conclusions : Our findings introduce a new tool for the stratification of ESD technical difficulty based on lesion size and morphological characteristics which could become crucial during the procedure's planning process.