Underestimation of the horizontal extent of ulcerative colitis-associated neoplasia may lead to incomplete endoscopic resection and subsequent recurrence.

Background: Endoscopic resection (ER) is increasingly utilized for ulcerative colitis-associated neoplasias (UCANs); however, these lesions demonstrate higher rates of local residuals and recurrences compared with sporadic neoplasias. This may be partly explained by challenges in accurately delineating lesion borders preoperatively, though their clinicopathologic features remain incompletely understood. Objectives: This study aimed to characterize the endoscopic and histologic features associated with local residuals and recurrences following ER for UCAN. Design: A retrospective observational study. Methods: Patients diagnosed with UCAN exhibiting a p53 mutation pattern between 2005 and 2024 and suspected of having local residual or recurrent lesions after ER were included. Endoscopic and histologic features were evaluated. Results: Of 122 UCAN patients, 13 (6 underwent initial ER at our institution before 2018, and 7 underwent initial ER elsewhere) were identified with suspected local residuals or recurrences. Prior to initial ER, p53 immunostaining was not performed in eight cases (five without biopsy and three with biopsy specimens not stained), and only two patients underwent biopsy of the surrounding tissue. Ten tumors had positive or potentially positive horizontal margins (HMs) that were not identified endoscopically at the time of ER. All local recurrences were associated with suspected positive HMs, with a median time to recurrence of 16.5 (8.5-23.8) months. At recurrence, 50% of the lesions appeared flat, while the remaining 50% were superficial elevated lesions with adjacent flat dysplasia. Conclusion: Inadequate preoperative assessment of the horizontal extent of UCANs may contribute to residual or recurrent disease after ER. Comprehensive evaluation-including p53 immunostaining and careful inspection for surrounding flat dysplasia-may improve curative outcomes in UCAN management.