What is the primary site of origin for carcinoid tumors with the highest rate of metastasis: appendix, bronchus (tracheobronchial tree), ileum, or stomach?

From the Guidelines

The highest rate of metastasis occurs in carcinoid tumors arising from the ileum (option c). According to the most recent and highest quality study 1, the overall frequency of primary neuroendocrine tumours of the gut and its adnexa, with percentage at each site presenting with metastases, shows that the ileum has a high rate of nodal and liver metastases, with 60% of cases presenting with nodal metastases and 30% with liver metastases. This is consistent with the fact that ileal carcinoids have an intermediate to high metastatic potential compared to other locations such as the appendix or stomach. The study also shows that the bronchus has a lower rate of metastasis, with 15% of cases presenting with nodal metastases and 5% with liver metastases, which contradicts the idea that bronchial carcinoids have the highest rate of metastasis. Additionally, the stomach has a relatively low rate of metastasis, with 35% of cases presenting with nodal metastases and 15% with liver metastases. Therefore, based on the most recent and highest quality evidence, the ileum is the location with the highest rate of metastasis for carcinoid tumors. Key points to consider include:

• The ileum has a high rate of nodal and liver metastases, with 60% of cases presenting with nodal metastases and 30% with liver metastases 1.
• The bronchus has a lower rate of metastasis, with 15% of cases presenting with nodal metastases and 5% with liver metastases 1.
• The stomach has a relatively low rate of metastasis, with 35% of cases presenting with nodal metastases and 15% with liver metastases 1.
• The appendix has a low rate of metastasis, with 5% of cases presenting with nodal metastases and 2% with liver metastases 1.

From the Research

Metastasis Rates in Carcinoid Tumors

• The highest rate of metastasis in carcinoid tumors is a critical factor in determining the appropriate treatment approach.
• Studies have shown that the location of the carcinoid tumor plays a significant role in determining the metastasis rate.
• According to the available evidence, carcinoid tumors arising from the ileum have a higher rate of metastasis compared to other locations such as the appendix, bronchus, or stomach 2, 3.
• A study published in 1983 found that patients with symptomatic carcinoid tumors of the ileum almost invariably had metastatic disease, with a 5-year actuarial survival rate of only 31% 2.
• Another study published in 1994 noted that small bowel carcinoid tumors, including those in the ileum, metastasize in 20-30% of cases if the tumor is smaller than 1 cm, highlighting the need for wide resection and regional lymph node removal 3.

Comparison of Metastasis Rates

• In contrast, carcinoid tumors of the appendix less than 1 cm in size do not metastasize, and an appendectomy is often the treatment of choice 3.
• Carcinoid tumors of the stomach and rectum less than 2 cm in size rarely metastasize, and local excision is often sufficient 4, 3.
• Carcinoid tumors of the bronchus are not specifically mentioned in the provided studies as having a high rate of metastasis.

Clinical Implications

• The high metastasis rate in ileal carcinoid tumors emphasizes the importance of early detection and treatment, such as wide resection and regional lymph node removal 2, 3.
• The use of ileoscopy during screening colonoscopy has been shown to improve long-term prognosis in patients with locally invasive ileal carcinoid tumors by allowing for early detection and treatment 5.