Do Appendiceal Neuroendocrine Tumors Metastasize Post Appendectomy or Right Hemicolectomy?

Background: Neuroendocrine tumors (NETs) of the appendix are typically detected incidentally during appendectomy. Recent studies reported no metachronous metastases among patients with primary tumors <2 cm, regardless of lymph node status or referral for completion hemicolectomy. However, questions persist regarding the possibility of metastases developing decades after surgical resection, particularly because appendiceal NETs are frequently diagnosed in young adults and children. Therefore, we sought to evaluate patients with metastatic appendiceal NETs to assess whether any had been diagnosed previously with an early-stage appendiceal NET.

Methods: We analyzed a large institutional neuroendocrine tumor database to identify appendiceal NETs of all stages and ascertain whether any patients with localized tumors developed metastases and whether any with metastatic disease had initially presented with an early-stage tumor.

Results: Of 3,795 patients with gastroenteropancreatic (GEP) NETs seen in an oncologic NET clinic between January 2008 and August 2023, 124 presented with appendiceal NETs. Of these, only 10 (<0.3% of the total GEP-NET population) had stage IV disease, 8 of whom were diagnosed synchronously at the time of initial diagnosis. Two patients with metastatic disease had reportedly undergone surgical resection for a primary appendiceal NET approximately 20 years before the diagnosis of metastatic disease, but medical records were not available to confirm an appendiceal primary.

Conclusions: Stage IV appendiceal NETs are exceptionally rare, and distant metastases are synchronous in nearly all cases. The risk of metastatic spread after resection of local appendiceal NETs is negligible. Patients with tumors <2 cm should not be managed with completion right hemicolectomy, and the role of this operation for larger tumors is questionable. Postoperative surveillance is unlikely to be of benefit.