Rectal neuroendocrine tumors in a colon cancer screening colonoscopy program. Sixteen-year single institution experience.

[OBJECTIVES] Rectal neuroendocrine tumors (rNETs) are potentially malignant lesions. In our study, we aimed to retrospectively check whether the rectal neuroendocrine tumors were found in colonoscopy examinations carried out as a part of Polish colonoscopy screening program (PCSP).

[MATERIALS AND METHODS] We retrospectively analyzed the colonoscopy and histopathological database of examinations conducted as a part of PCSP in our institution in the years 2005-2021. We also checked the method by which the tumor was removed, its characteristics based on photo documentations and followed up the patients.

[RESULTS] The 10568 colonoscopy examinations were performed in PCSP in the years 2005-2021. Seven patients with a mean age of 53 with rNETs (1 in every 1510 colonoscopy) were detected. The polyp mean size was 5 mm. All the lesions were well differentiated tumors. First half of the colonoscopy examinations was performed in the years 2005-2012 and in that time three rNETs were detected, four rNETs were detected in the years 2012-2021. Even despite their typical appearance the neuroendocrine origin was not suspected in majority of cases and all tumors, except one, were removed with improper method. One of the patients underwent transanal endoscopic microsurgery of the scar. All patients are disease free in median follow-up of 108 months.

[CONCLUSION] Rectal NETs are detected in the screening colonoscopy program. In majority of cases, they are not suspected by endoscopists on colonoscopy, but diagnosed after removal in histopathological examinations. There is a need of education of endoscopists in recognition and methods of treatment of rNETs.