From the Research
The mechanism of spread from a neuroendocrine tumor (NET) in the ileum to lymph nodes and liver involves both lymphatic and hematogenous pathways, with lymphatic spread to regional mesenteric lymph nodes and hematogenous spread through the portal venous system to the liver. Ileal NETs initially spread via lymphatic vessels to regional mesenteric lymph nodes, particularly those in the ileocecal region, as tumor cells invade local lymphatic vessels and are carried to nearby nodes 1. For liver metastasis, the primary mechanism is hematogenous spread through the portal venous system, where tumor cells enter the mesenteric veins that drain into the portal vein, providing direct access to the liver 2. This explains why the liver is the most common site of distant metastasis for ileal NETs. The rich dual blood supply of the liver (portal venous and hepatic arterial) creates an environment conducive to metastatic growth. Additionally, ileal NETs often produce vasoactive substances like serotonin, which normally would be metabolized by the liver but can cause carcinoid syndrome when liver metastases allow these substances to bypass hepatic metabolism and enter systemic circulation.
Some key points to consider in the mechanism of spread include:
- The size of the tumor does not necessarily dictate the risk of metastasis, as tumors as small as 3 mm can give rise to nodal metastasis 1
- The lymphatic route is an important pathway for peritoneal dissemination, even in early stages of gastric cancer 3
- Hematogenous spread through the portal venous system is a primary mechanism for liver metastasis in colorectal cancer 2
- The tumor microenvironment, including factors such as integrins and exosomal integrins, cancer stem cell phenotype, and miRNA expression, can contribute to the metastatic route 2
Overall, understanding the mechanisms of metastasis in ileal NETs is crucial for developing effective treatment strategies and improving patient outcomes.