Neuroendocrine Tumors: Hormone Symptoms, Imaging, and Treatment Choices

Neuroendocrine tumors are uncommon cancers that start in hormone-producing neuroendocrine cells and can appear in many organs, especially the digestive system, pancreas, and lungs. Symptoms, imaging tests, and treatment choices vary widely, so careful diagnosis by an experienced multidisciplinary team is important.

Overview

Neuroendocrine tumors, often called NETs, begin in neuroendocrine cells. These cells share features of nerve cells and hormone-producing endocrine cells, helping the body regulate digestion, breathing, blood sugar, and other functions. NETs can develop in many parts of the body, but they are most often found in the gastrointestinal tract, pancreas, and lungs.

NETs are a diverse group of tumors. Some grow very slowly over years, while others behave more aggressively. Doctors describe them by their location, whether they produce hormones, how far they have spread, and how the tumor cells look under a microscope. The grade, which reflects how quickly the cells are dividing, is especially important for treatment planning.

The term carcinoid tumor is sometimes used for certain well-differentiated NETs, especially those arising in the small intestine, appendix, rectum, or lung. However, modern medical language usually uses neuroendocrine tumor for well-differentiated tumors and neuroendocrine carcinoma for high-grade, poorly differentiated cancers. This distinction matters because the expected behavior and treatment choices can be quite different.

Hormone Symptoms and Common Signs

Symptoms of neuroendocrine tumors depend on where the tumor is located, whether it releases active hormones, and whether it has spread. Many NETs are nonfunctional, meaning they do not produce enough hormone to cause a recognizable syndrome. These tumors may cause vague symptoms such as abdominal discomfort, changes in bowel habits, cough, unexplained weight change, or may be found incidentally during imaging or endoscopy for another reason.

Functional NETs release hormones or hormone-like substances that can cause more specific symptoms. Carcinoid syndrome is one example, most often associated with serotonin-producing NETs that have spread to the liver or, less commonly, with lung NETs. It may cause episodes of facial flushing, diarrhea, abdominal cramping, wheezing, or a fast heartbeat. Long-standing carcinoid syndrome can sometimes affect heart valves, so doctors may recommend heart evaluation in selected patients.

Pancreatic neuroendocrine tumors may produce different hormone patterns. An insulin-producing tumor can cause low blood sugar with sweating, shakiness, confusion, or faintness. A gastrin-producing tumor can lead to recurrent stomach ulcers, acid reflux, or diarrhea. Other functional pancreatic NETs may cause skin rash, high blood sugar, watery diarrhea, dehydration, or changes in potassium levels. Because these symptoms can overlap with common conditions, diagnosis often requires targeted testing.

• Possible symptoms include flushing, diarrhea, wheezing, abdominal pain, nausea, ulcers, low blood sugar episodes, cough, fatigue, or unexplained weight loss.
• Symptoms may come and go, and some people have no symptoms at all.
• Any persistent, recurrent, or unexplained symptom should be discussed with a qualified doctor, especially if it is worsening or associated with weight loss, bleeding, fainting, or dehydration.

Causes and Risk Factors

For most people, the exact cause of a neuroendocrine tumor is not known. NETs develop when genetic changes in a neuroendocrine cell allow it to grow in an uncontrolled way. These changes usually happen during a person’s lifetime and are not inherited from a parent. Having a NET does not mean a patient did anything to cause it.

A small percentage of NETs are linked to inherited syndromes. These may include multiple endocrine neoplasia type 1, von Hippel-Lindau disease, neurofibromatosis type 1, or tuberous sclerosis complex. People with these conditions may develop endocrine or neuroendocrine tumors at younger ages or in multiple sites. Genetic counseling may be recommended when a patient has a strong family history, multiple tumors, early-onset disease, or clinical features suggesting an inherited syndrome.

Risk factors can also vary by tumor site. For example, some stomach NETs are associated with chronic atrophic gastritis or high gastrin levels. Lung neuroendocrine tumors have different subtypes; smoking is strongly linked with high-grade small cell and large cell neuroendocrine carcinomas, but less clearly with typical lung carcinoids. A patient’s overall history, imaging findings, pathology, and laboratory results help doctors understand the most likely tumor type.

Diagnosis and Staging

Diagnosis begins with a careful medical history, physical examination, and review of symptoms. If hormone-related symptoms are present, doctors may order blood or urine tests. These tests may include markers such as chromogranin A or specific hormones, but results can be affected by medicines, stomach acid conditions, kidney function, and other illnesses. For that reason, laboratory tests are interpreted alongside imaging and pathology rather than used alone.

A biopsy is often needed to confirm the diagnosis. A pathologist examines the tissue to determine whether the tumor is well differentiated or poorly differentiated, and to measure the Ki-67 index or mitotic rate, which helps define grade. Immunohistochemistry tests may look for markers such as synaptophysin and chromogranin. This pathology information guides treatment because a low-grade well-differentiated NET is managed differently from a high-grade neuroendocrine carcinoma.

Staging describes how far the tumor has spread. It may include the size of the primary tumor, involvement of nearby lymph nodes, and whether metastases are present in the liver, bones, lungs, or other organs. Accurate staging helps doctors decide whether surgery is possible, whether systemic treatment is needed, and how closely the patient should be followed over time.

Imaging Tests Used for NETs

Imaging is central to neuroendocrine tumor care. Contrast-enhanced CT scans are commonly used to evaluate the chest, abdomen, and pelvis. MRI is particularly useful for assessing the liver, pancreas, rectum, and certain soft-tissue details. Because many NETs are vascular tumors, scans may be timed to capture arterial and venous phases, improving the chance of seeing small lesions.

Specialized nuclear medicine imaging can provide information that standard scans may not show. Many well-differentiated NETs have somatostatin receptors on their surface. PET/CT using gallium-68 or copper-64 labeled somatostatin analog tracers can detect these receptors and help map disease throughout the body. This type of scan also helps determine whether peptide receptor radionuclide therapy, known as PRRT, may be an option.

Not every patient needs every imaging test. For higher-grade tumors, an FDG PET/CT may be helpful because it shows areas of higher glucose activity, which can correlate with more aggressive biology. Endoscopy, colonoscopy, bronchoscopy, endoscopic ultrasound, or capsule endoscopy may be used depending on the suspected tumor location. The best imaging plan is individualized to the tumor type, symptoms, kidney function, previous test results, and treatment goals.

Treatment Options

Treatment for neuroendocrine tumors is highly individualized. Surgery is often the preferred option when a tumor can be completely removed and the patient’s health allows an operation. Surgery may involve removing the primary tumor, affected lymph nodes, or selected metastases. In some patients with limited liver disease, surgery, ablation, or embolization procedures may help reduce tumor burden or hormone symptoms.

Medicines may be used to control hormone symptoms and slow tumor growth. Somatostatin analogs are commonly used for many well-differentiated NETs that express somatostatin receptors, especially when carcinoid syndrome is present or disease is advanced but slow-growing. Additional medicines may be used for specific symptoms, such as diarrhea related to carcinoid syndrome or acid overproduction in gastrinoma, depending on the patient’s condition and test results.

Systemic cancer treatments may include targeted therapies, chemotherapy, immunotherapy in selected high-grade cases, or PRRT for somatostatin receptor-positive disease. PRRT delivers radiation directly to tumor cells that carry somatostatin receptors and is considered for certain advanced well-differentiated NETs. Chemotherapy is more often used for pancreatic NETs with higher tumor burden or for poorly differentiated neuroendocrine carcinomas, where faster treatment response may be needed.

Because NETs vary widely, care is usually best planned by a multidisciplinary team that may include medical oncology, surgical oncology, gastroenterology, endocrinology, nuclear medicine, radiology, pathology, interventional radiology, and nutrition specialists. Treatment decisions consider tumor grade, stage, growth rate, hormone symptoms, somatostatin receptor status, prior treatments, overall health, and patient preferences.

Prevention, Self-Care, and Follow-Up

There is no proven way to prevent most neuroendocrine tumors. People with known hereditary syndromes may benefit from specialist surveillance plans, which can help detect tumors earlier. For the general population, the most practical approach is to seek medical evaluation for persistent unexplained symptoms and to keep recommended follow-up appointments if a NET has already been diagnosed.

Self-care focuses on supporting overall health and managing symptoms safely. Patients with hormone-related diarrhea, flushing, or blood sugar changes should ask their care team about dietary triggers, hydration, and when to seek urgent help. Some people notice that alcohol, large meals, spicy foods, stress, or certain medicines worsen flushing or diarrhea, but triggers differ from person to person. Any dietary changes should be balanced and discussed with a clinician, especially if weight loss or malnutrition is present.

Follow-up may include periodic imaging, blood or urine markers, symptom review, and assessment of treatment side effects. The schedule depends on the tumor type, grade, stage, and treatment history. Even slow-growing NETs can recur or progress after long quiet periods, so regular monitoring is important. Patients should keep copies of pathology reports, imaging summaries, and treatment records, particularly if they seek care across different hospitals or countries.

When to See a Doctor

A person should speak with a doctor if they have persistent or recurrent flushing, unexplained diarrhea, wheezing without a clear cause, repeated low blood sugar symptoms, recurrent stomach ulcers, unexplained abdominal pain, rectal bleeding, a new persistent cough, or unintentional weight loss. These symptoms do not necessarily mean cancer, but they deserve medical assessment when they continue, worsen, or affect daily life.

People already diagnosed with a neuroendocrine tumor should contact their care team if symptoms suddenly increase, diarrhea causes dehydration, fainting occurs, blood sugar becomes difficult to control, pain worsens, jaundice develops, or new shortness of breath appears. During treatment, patients should also report side effects promptly so that supportive care can be adjusted.

International patients may benefit from coordinated evaluation where imaging, pathology, surgery, oncology, nuclear medicine, and supportive care are available in one pathway. Acibadem International provides multidisciplinary assessment and treatment for neuroendocrine tumors in JCI-accredited hospitals, with care planning guided by the patient’s diagnosis and medical needs.

Frequently asked questions

Are neuroendocrine tumors always cancer?

Neuroendocrine tumors are generally considered malignant because they have the potential to grow, invade, or spread, but many are slow-growing. Their behavior depends on grade, stage, location, and cell differentiation. A pathology report is essential for understanding the individual risk.

What is carcinoid syndrome?

Carcinoid syndrome is a group of symptoms caused by hormones or hormone-like substances released by some neuroendocrine tumors. It may include flushing, diarrhea, wheezing, abdominal cramping, or a fast heartbeat. It is most often seen when serotonin-producing tumors have spread to the liver, but patterns can vary.

Which scan is best for neuroendocrine tumors?

There is no single best scan for every patient. CT and MRI are commonly used to define anatomy, while somatostatin receptor PET/CT can be very helpful for many well-differentiated NETs. FDG PET/CT may be useful for higher-grade or more aggressive tumors.

Can a neuroendocrine tumor be cured with surgery?

Surgery can be curative when the tumor is localized and can be completely removed. If the tumor has spread, surgery may still help selected patients by reducing tumor burden or controlling symptoms. The decision depends on tumor location, spread, grade, and the patient's overall health.

Do all neuroendocrine tumors need chemotherapy?

No. Many well-differentiated, slow-growing NETs are treated with surgery, somatostatin analogs, targeted therapy, PRRT, liver-directed therapy, or careful monitoring rather than traditional chemotherapy. Chemotherapy is more commonly used for high-grade neuroendocrine carcinomas or selected pancreatic NETs.

How often should patients be followed after treatment?

Follow-up schedules vary based on tumor grade, stage, treatment, and risk of recurrence. Many patients need periodic imaging and laboratory tests for years because NETs can grow slowly. The treating specialist can recommend an individualized surveillance plan.

References

• World Health Organization
• National Cancer Institute
• European Society for Medical Oncology
• North American Neuroendocrine Tumor Society
• European Neuroendocrine Tumor Society

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.