Intestinal neuroendocrine tumors (carcinoid)

What neuroendocrine tumors are

These tumors arise from neuroendocrine cells scattered through the bowel wall, which produce hormone-like substances, notably serotonin. In the intestine they most often occur in the ileum, appendix and rectum; less often in the duodenum and colon. The cause of most of them is unknown; some are linked to hereditary syndromes, in particular multiple endocrine neoplasia type 1.

The key feature of the tumor is its grade (G1–G3), determined by the Ki-67 index and mitotic count: G1 tumors grow the slowest and G3 the fastest. Neuroendocrine carcinoma is a separate category — an aggressive tumor treated differently from ordinary neuroendocrine tumors.

Are there symptoms

Appendiceal and rectal tumors usually cause no symptoms. Ileal tumors may show up for years as intermittent abdominal pain attributed to a “sensitive bowel”; sometimes the first sign is obstruction or impaired blood supply to the bowel caused by scarring of the mesentery around metastatic lymph nodes.

Carcinoid syndrome — episodes of flushing of the face and neck, diarrhea, sometimes wheezing — occurs mainly when there are liver metastases. Over time it can damage the heart valves, so these patients need echocardiography.

Examinations needed

• Pathology report with the Ki-67 index and grade — treatment cannot be planned without it.
• Somatostatin receptor PET-CT (for example, with ⁶⁸Ga-DOTATATE) — a highly sensitive method for finding the primary tumor and metastases of well-differentiated tumors; it also shows whether the tumor can be treated with drugs acting through somatostatin receptors.
• Contrast-enhanced CT of the abdomen and pelvis and liver MRI — to assess the mesentery, lymph nodes and liver metastases.
• 24-hour urinary 5-HIAA — for small bowel tumors and symptoms of carcinoid syndrome.
• Echocardiography — with carcinoid syndrome or high 5-HIAA levels.
• Colonoscopy; for rectal tumors — endoscopic ultrasound or pelvic MRI.

When surgery is possible

For small bowel tumors, surgery is usually recommended in patients who can tolerate it: even with liver metastases, removing the primary tumor with its mesentery is often considered, because it lowers the risk of obstruction and loss of blood supply to the bowel.

Appendiceal tumors under 1 cm removed with the appendix usually need no further surgery. Tumors over 2 cm are an indication for right hemicolectomy with lymph nodes; for tumors of 1–2 cm it is discussed individually based on risk factors — mesoappendiceal invasion over 3 mm, vascular invasion, grade G2, location at the base of the appendix, a positive margin.

Rectal tumors under 1 cm, grade G1, not invading the muscle layer are removed endoscopically. Tumors over 2 cm, invading the muscle layer or with lymph node involvement are operated on as rectal cancer; for tumors of 1–2 cm the approach is decided individually — by endoscopic ultrasound, MRI, grade and signs of invasion.

Liver metastases from G1–G2 tumors are removed when all or the vast majority of lesions can be cleared — see the liver metastases from other tumors page for details.

If surgery is not possible now

For well-differentiated tumors, treatment is usually based on somatostatin analogs — injections every few weeks that slow tumor growth and relieve carcinoid syndrome. If the tumor progresses, options include radionuclide therapy with agents taken up by cells with somatostatin receptors, targeted drugs, and, for neuroendocrine carcinomas, chemotherapy; G3 tumors are treated with separate regimens.

Because these tumors often grow slowly, in selected patients the MDT may reassess the possibility of surgery after a response to treatment.

How the operation is performed

For a small bowel tumor, the bowel segment is removed together with the mesentery and lymph nodes, preserving the vessels that supply the rest of the bowel. Small bowel tumors are often multiple and tiny, so the entire small bowel is inspected and palpated during surgery. For appendiceal tumors, when indicated, and tumors of the right colon, a right hemicolectomy is performed; for large or invasive rectal tumors — resection with the mesorectum, as for cancer.

Patients with carcinoid syndrome receive a somatostatin analog before surgery to lower the risk of a carcinoid crisis — sharp swings in blood pressure, bronchospasm and rhythm disturbances during the operation. When the tumor’s location and the extent of resection allow, the operation is performed laparoscopically, through several small incisions.

Recovery after surgery

Care follows the enhanced recovery after surgery (ERAS) protocol: early mobilization, early feeding, controlled pain relief. After resection of a small bowel segment or right hemicolectomy, digestion usually recovers, although bowel habits may change; after removal of the terminal ileum, vitamin B12 levels are monitored.

Adjuvant chemotherapy is usually not needed after complete removal of a G1–G2 neuroendocrine tumor. Patients on long-term somatostatin analogs have their gallbladder monitored, because these drugs promote gallstone formation.

Follow-up

Follow-up lasts for years — longer than for most other tumors, because recurrences can appear late. CT or MRI is used, and when indicated, somatostatin receptor PET-CT and 5-HIAA; the doctor sets the intervals according to tumor grade. After endoscopic removal of a G1 rectal tumor under 1 cm with clear margins or appendectomy for a tumor under 1 cm, minimal follow-up is usually enough.

What to bring to the consultation

• the pathology and immunohistochemistry report with the Ki-67 index and grade;
• tissue blocks and slides — for review by another laboratory;
• CT, MRI and PET-CT discs with reports;
• the operative or endoscopic removal report, if the tumor has already been removed;
• 5-HIAA and chromogranin A results, echocardiography results, if performed;
• a list of your medications, including somatostatin analogs.

If some materials are missing, that is no reason to postpone the consultation: some examinations can be done on site.

The consultation is free of charge. How it goes and how long it takes is described on the page “Oncologist Consultation”.