Abstract Objectives Endoscopic submucosal dissection (ESD) enables en bloc resection of colorectal neoplasms, but occasionally results in positive horizontal margins (HMs). However, the site of the resected specimen that tends to be positive for HM has not been investigated. We aimed to clarify the characteristics associated with HMs in lesions resected en bloc with ESD. Methods Patients with colorectal neoplasms who underwent en bloc resection with ESD were included in this study. The patients were divided into negative HMs (HM0) and positive or indeterminate HMs (HM1) groups. The characteristics associated with HM1 resection were investigated. In addition, the local recurrence rate during endoscopic follow‐up for >6 months after ESD was observed. Results In total, 201 lesions were analyzed in 189 patients (HM0, 189 lesions; HM1, 12 lesions). The HM1 group had a significantly larger median lesion diameter (25 vs. 55 mm; p 50% circumference than did the HM0 group (p 50% circumference, and submucosal fibrosis.
