1194P - Do metastatic appendiceal NETs ever develop metachronously after appendectomy or right hemicolectomy?

Background

Neuroendocrine tumors of the appendix are typically detected incidentally during appendectomy. A recent study reported no cases of metachronous metastases among patients with primary tumors <2cm, regardless of lymph node status or referral for completion hemicolectomy. However, questions persist regarding the possibility of metastases developing decades after surgery, particularly since appendiceal NETs are frequently diagnosed in young adults and children.We therefore 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 originally presented with an early-stage tumor.

Results

Out of over 5,000 patients seen in the neuroendocrine tumor clinic between 2008 and 2022, 95 were diagnosed with an appendiceal NET. Of these, only 6 patients (approximately 0.1% of total NET population) had stage 4 metastases, all diagnosed synchronously at time of initial diagnosis. All 6 patients had peritoneal disease. No patient with earlier-stage disease developed distant metastases.

Conclusions

Metastatic appendiceal NETs are exceptionally rare with a tendency to metastasize within the peritoneum. In all cases of stage 4 disease, metastases were observed at time of diagnosis. Our data provide further validation for the proposition that small local appendiceal NETs resected during appendectomy require no further surgery or surveillance.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

J. Strosberg: Financial Interests, Personal, Speaker’s Bureau: Ipsen, Tersera; Financial Interests, Personal, Speaker, Consultant, Advisor: Novartis. All other authors have declared no conflicts of interest.