Understanding Neuroendocrine Tumours: Types and Symptoms
Learn about neuroendocrine tumours (NETs), their types, symptoms, and how they affect the body. Understand functional vs. nonfunctional NETs, growth patterns, and common locations like the gastrointestinal tract, pancreas, and lungs.
Written by Dr.Sonia Bhatt
Last updated on 3rd Jul, 2025
Introduction
Neuroendocrine tumours (NETs) are a diverse group of neoplasms that arise from neuroendocrine cells, which have traits similar to both nerve cells and hormone-producing endocrine cells. These tumours can occur anywhere in the body but are most commonly found in the gastrointestinal tract, pancreas, and lungs. NETs can be either benign or malignant, and their behaviour can range from slow-growing to highly aggressive. This article provides a comprehensive overview of the types and symptoms of neuroendocrine tumours, helping individuals recognise potential warning signs and seek timely medical attention.
Types of Neuroendocrine Tumours
Neuroendocrine tumours are classified based on their hormone production, growth rate, and location. Here are the main types of NETs:
1. Based on Hormone Production: Functional vs. Nonfunctional Neuroendocrine Tumours (NETs)
Neuroendocrine tumours (NETs) are classified into two main categories based on their ability to produce hormones: functional and nonfunctional. Understanding the distinction between these two types is crucial for proper diagnosis and treatment planning.
Functional NETs:
Functional NETs are characterised by their ability to produce and secrete hormones. These hormones can lead to a variety of symptoms, often dependent on the type of hormone overproduced. Functional NETs can occur in various organs, including the gastrointestinal tract, pancreas, lungs, and other locations. For example, insulinomas produce excess insulin, leading to hypoglycemia (low blood sugar).
Nonfunctional NETs:
Nonfunctional NETs do not produce excessive hormones that result in recognisable symptoms. This makes them challenging to detect in the early stages. Instead, their impact is often related to the size and location of the tumour. Nonfunctional NETs can also occur in various organs, including the gastrointestinal tract, pancreas, lungs, and other locations.
2. Based on Growth Rate: Indolent vs. Aggressive Neuroendocrine Tumours (NETs)
Neuroendocrine tumours (NETs) can be classified based on their growth rate and cellular characteristics into two main categories: indolent and aggressive. Understanding the differences between these two types is crucial for proper diagnosis, treatment planning, and prognosis.
Indolent NETs:
Indolent NETs are characterised by their slow growth and well-differentiated cells, which resemble normal, noncancerous cells. These tumours are often referred to as low-grade NETs and have a lower risk of spreading (metastasising) to other parts of the body.
Aggressive NETs:
Aggressive NETs are characterised by their rapid growth and poorly differentiated cells, which look very different from normal, noncancerous cells. These tumours are often referred to as high-grade NETs and have a higher risk of spreading to other parts of the body.
3. Based on Location:
3.1 Gastroenteropancreatic Neuroendocrine Tumours (GEP-NETs)
Gastroenteropancreatic neuroendocrine tumours (GEP-NETs) are a subset of neuroendocrine tumours that arise from the neuroendocrine cells within the gastrointestinal tract and pancreas. These tumours can be either benign or malignant and can produce a variety of hormones, leading to distinct clinical syndromes. GEP-NETs are further classified based on their location within the gastrointestinal tract or pancreas.
Gastrointestinal Neuroendocrine Tumours (GI-NETs):
Stomach (Gastric NETs): These tumours develop in the stomach lining and can produce hormones such as gastrin, leading to conditions like Zollinger-Ellison syndrome. Symptoms may include abdominal pain, nausea, vomiting, and gastrointestinal bleeding.
Small Intestine (Enteric NETs): These tumours are commonly found in the small intestine, particularly in the ileum. They can produce serotonin and other hormones, leading to carcinoid syndrome. Symptoms may include abdominal pain, diarrhoea, flushing, and heart valve problems.
Appendix (Appendiceal NETs): These tumours are often discovered incidentally during appendectomies. They are usually small and slow-growing, with symptoms that may include abdominal pain and carcinoid syndrome in rare cases.
Colon and Rectum (Colorectal NETs): These tumours develop in the colon or rectum and can produce hormones such as serotonin. Symptoms may include changes in bowel habits, rectal bleeding, and abdominal pain.
Pancreatic Neuroendocrine Tumours (P-NETs):
Insulinomas: These tumours produce excess insulin, leading to hypoglycemia (low blood sugar). Symptoms may include sweating, confusion, dizziness, and fainting.
Gastrinomas: These tumours produce excess gastrin, leading to Zollinger-Ellison syndrome. Symptoms may include severe gastric ulcers, abdominal pain, and diarrhoea.
Glucagonomas: These tumours produce excess glucagon, leading to hyperglycemia (high blood sugar). Symptoms may include weight loss, rash (necrolytic migratory erythema), and diabetes.
VIPomas: These tumours produce vasoactive intestinal peptides (VIP), leading to severe watery diarrhoea, dehydration, and electrolyte imbalances.
Somatostatinomas: These tumours produce excess somatostatin, leading to symptoms such as diabetes, gallstones, and steatorrhea (fatty stools).
3. 2 Pulmonary Neuroendocrine Tumours
Pulmonary neuroendocrine tumours (NETs) are a subset of neuroendocrine tumours that originate in the lungs or bronchi, the tubes that carry air from the windpipe to the lungs. These tumours are relatively rare and can vary in their behaviour, ranging from slow-growing to highly aggressive. Pulmonary NETs are classified into four main types based on their growth rate and cellular characteristics:
Typical Carcinoids: These tumours are the most common type of pulmonary NETs. They are generally slow-growing and less likely to spread to other parts of the body. Symptoms may include persistent coughing, wheezing, shortness of breath, and chest pain. Some patients may also experience hemoptysis (coughing up blood).
Atypical Carcinoids: These tumours are less common than typical carcinoids and tend to grow more rapidly. They have a higher likelihood of spreading to other parts of the body. Symptoms may include persistent coughing, wheezing, shortness of breath, chest pain, and hemoptysis. Patients may also experience symptoms related to hormone production, such as flushing and diarrhoea.
Large Cell Neuroendocrine Carcinomas (LCNEC): These tumours are rare and aggressive. They grow rapidly and have a high potential for metastasis (spreading to other parts of the body). Symptoms may include persistent coughing, wheezing, shortness of breath, chest pain, weight loss, and fatigue. Due to their aggressive nature, these tumours can cause significant respiratory symptoms and systemic effects.
Small Cell Lung Cancer (SCLC): These tumours are highly aggressive and fast-growing. They are often associated with smoking and have a high potential for metastasis. Symptoms may include persistent coughing, wheezing, shortness of breath, chest pain, weight loss, fatigue, and hemoptysis. Patients may also experience paraneoplastic syndromes, which are symptoms caused by hormone production from the tumour, such as Cushing's syndrome and SIADH (syndrome of inappropriate antidiuretic hormone secretion).
3.3 NETs in Other Organs
Neuroendocrine tumours (NETs) can develop in various organs outside the gastrointestinal tract, pancreas, and lungs. These tumours are relatively rare and can produce a variety of hormones, leading to distinct clinical syndromes. Here are the main types of NETs that can occur in other organs:
Thyroid NETs: These tumours develop in the thyroid gland, which is located in the neck and produces hormones that regulate metabolism. Symptoms may include a lump in the neck, difficulty swallowing, hoarseness, and changes in thyroid hormone levels, leading to symptoms such as weight changes, fatigue, and temperature sensitivity.
Parathyroid NETs: These tumours originate in the parathyroid glands, which are small glands located near the thyroid gland and regulate calcium levels in the blood. Symptoms may include elevated calcium levels (hypercalcemia), leading to symptoms such as kidney stones, bone pain, abdominal pain, and fatigue.
Pituitary NETs: These tumours develop in the pituitary gland, which is located at the base of the brain and produces hormones that regulate various bodily functions. Symptoms may include headaches, vision problems, and hormone imbalances, leading to symptoms such as menstrual irregularities, growth abnormalities, and changes in libido.
Adrenal NETs: These tumours originate in the adrenal glands, which are located on top of each kidney and produce hormones such as cortisol, aldosterone, and adrenaline. Symptoms may include high blood pressure, weight gain, muscle weakness, and hormone-related changes such as Cushing's syndrome (excess cortisol) or Conn's syndrome (excess aldosterone).
Thymus NETs: These tumours develop in the thymus gland, which is located in the upper chest and plays a role in the immune system. Symptoms may include chest pain, cough, difficulty breathing, and symptoms related to hormone production, such as flushing and diarrhoea.
Merkel Cell Carcinoma: A rare and aggressive form of skin cancer that originates from neuroendocrine cells in the skin. Symptoms may include a fast-growing, painless nodule on the skin, often appearing as a red or purple bump. The tumour can spread to other parts of the body, leading to additional symptoms.
Conclusion
Neuroendocrine tumours are a diverse group of neoplasms that can cause a wide range of symptoms depending on their hormone production, growth rate, and location. Recognising the symptoms of NETs is crucial for early diagnosis and treatment. If you experience persistent symptoms such as abdominal pain, unexplained weight loss, or hormone-related changes, it is important to consult a healthcare provider for proper evaluation and management. Early detection and treatment can improve the prognosis for individuals with neuroendocrine tumours and help manage the symptoms effectively.
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