Background: Appendiceal neuroendocrine tumors (ANETs) less than 2 cm were thought to have no metastatic potential; however, recent evidence including our previous report shows increasing occurrences of regional and metastatic disease in smaller ANETs. We provided an update of patients with ANETs at our institution.

Methods: A retrospective review was performed in a follow-up series of patients with ANET who presented to our tertiary referral center from 2019-2020. Demographics, tumor characteristics, treatment, and clinical outcomes were evaluated.

Cohort update: In total, 36 patients were included and compared to our previous 114 patients with ANETs who underwent surgical resection. In this updated cohort, we again showed that regional and distant spread is a rare event but can occur in ANETs less than 2 cm. We then discussed the importance of ANET biological factors such as invasion depth, tumor grade, and small vessel invasion and the risk of aggressive disease. Furthermore, we discussed the relevance of lymph node involvement and distant disease as well as the effect of metastasis on outcomes. Lastly, we summarize the work-up and management of a patient with incidental ANET following appendectomy.

Conclusions: The complexity of ANET management stems from their incidental discovery, rarity, and overall excellent survival. ANETs less than 2 cm may have metastatic potential and seem to be driven by biological factors such as small vessel invasion, invasion depth, and tumor grade more than primary tumor size. Metastatic disease is the main determinant of survival, whereas the management of regional lymph node metastasis with RH has unproven benefit on long-term outcomes. Patients should be evaluated with individualized care focusing on clinical and pathological risk factors for more aggressive disease which should guide management and surveillance.