Gastrointestinal neuroendocrine tumors

Gastrointestinal neuroendocrine tumors (GI NETs) are a type of tumor that develops in the digestive tract. They can form anywhere from the esophagus to the anus. Most often, they form in the small intestine (small bowel) or mesentery, the tissue that secures the intestines to the belly’s wall. Another common location is the rectum, the last section of the large intestine (large bowel).

When neuroendocrine tumors form in the GI tract, the most effective care comes from a team that’s used to seeing complex cases. At Penn Medicine, our experts regularly treat a wide range of GI NETs, including tumors that release hormones or spread to the liver. We’re known for advanced surgery, research into new therapies, and long-term support focused on symptom relief and quality of life.

While various types of neuroendocrine tumors can occur throughout the body, they form most frequently in the GI tract.

Doctors distinguish gastrointestinal neuroendocrine tumors by their:

• Frequency: With roughly 8,000 people in the U.S. diagnosed a year, GI NETs are fairly rare. But they’re still the second-most common GI tumor after colorectal cancer.
• Hormone potential: Most GI NETs are carcinoid tumors, which may release hormones that cause symptoms. A less common type, called a gastrinoma, releases the hormone gastrin.
• Behavior: Like other neuroendocrine tumors, most GI carcinoids grow slowly. They often metastasize (spread) but it may take years. The most common locations of metastatic GI carcinoids are the lymph nodes and liver, followed by the bones and lungs. While tumors can spread when fairly small, they can also grow quite large before doing so.
• Appearance: The cells of GI carcinoids look like normal cells (well-differentiated). The cells of a much less common NET, GI neuroendocrine carcinoma, appear very different. These poorly differentiated tumors, also called NECs, act more aggressively and pose a greater treatment challenge.

Doctors typically don’t know why a GI NET forms. They have identified one possible risk factor for stomach NETs — diseases that reduce stomach acid. Penn Medicine offers genetic testing for neuroendocrine tumors to help assess risk.

Some GI NETs are linked to inherited genetic variants passed down through families. Penn Medicine offers genetic testing for neuroendocrine tumors and genetic counseling to help identify inherited conditions and guide care for you and your family.

Variants in these genes may raise the risk for certain tumors:

• MEN1: These variants lead to multiple endocrine neoplasia type 1, or MEN1. People with the condition are much more likely to develop a range of tumors, including gastrinoma in the duodenum, the small intestine’s first section. They’re also at higher risk for lung neuroendocrine tumors and pancreatic neuroendocrine tumors.
• NF1: These variants cause neurofibromatosis type 1, or NF1. The condition features an increased risk of a GI carcinoid in the duodenum. People with NF1 can also develop an adrenal gland NET called a pheochromocytoma.

Care for these tumors is complex. To get an accurate diagnosis and a treatment plan that’s right for you, you need a team that understands the nuances of GI NETs. At Penn Medicine, our specialists meet every week to collaborate on your care and agree on the best next steps. This level of coordination ensures you’re getting the benefit of many experts at once.

Because many GI NETs grow slowly, care often involves managing symptoms and adjusting treatment over time. In addition to offering a full range of therapies and clinical trials, we provide GI symptom management for neuroendocrine tumors and support services to help you and your family navigate every step.