Appendiceal Neuroendocrine Tumor: Clinicopathologic Characteristics of Six Cases and Review of the Literature.

Background/aim: Appendiceal neuroendocrine tumors (ANETs) are the most prevalent type of appendiceal neoplasm and the fifth most common neuroendocrine tumor in the gastrointestinal tract. In this study, we described the clinicopathological features of patients with ANET.

Patients and methods: We reviewed the clinicopathological findings and histopathological reports of six patients diagnosed with ANET between January 2014 and December 2023 at Korea University Medical Center, Anam Hospital.

Results: Six cases, comprising three males and three females, were diagnosed during procedures for lower abdominal pain or other medical reasons. Most tumors were less than 1 cm in size and located at the tip of the appendix. One patient had a large tumor (4.1 cm) with lymph node metastasis. Four tumors extended to the muscularis propria, whereas two infiltrated the subserosal soft tissue. The tumor cells exhibited a typical trabecular and nested pattern with monotonous round or oval nuclei. All patients had a mitotic count of less than 2 per 10 high-power fields and a Ki-67 labeling index of less than 1%, classifying them as having G1 well-differentiated tumors. Immunohistochemical staining showed that all cases were positive for CD56 and synaptophysin, and four were positive for chromogranin A. No recurrence or distant metastasis was observed during follow-up.

Conclusion: ANETs are relatively uncommon and mostly benign in terms of prognosis. Because of their malignant potential, meticulous examination of appendectomy specimens is warranted to identify the presence of ANETs.