Neuroendocrine cells are specialized cells found throughout the body that possess characteristics of both nerve cells and hormone-producing cells. These cells act as a bridge between the body’s nervous system and its endocrine (hormone) system. They function much like translators, receiving signals from the nervous system and then converting these messages into chemical signals. These hormones are then released into the bloodstream to carry out various regulatory functions.
Role in the Body
Neuroendocrine cells are scattered throughout various tissues, forming what is known as the diffuse neuroendocrine system. This widespread distribution allows them to exert localized and systemic control over bodily processes.
In the gastrointestinal tract, neuroendocrine cells are embedded within the organ lining, where they regulate digestion. They control the secretion of digestive juices and influence the muscle contractions that move food through the gut.
Pulmonary neuroendocrine cells (PNECs) are found in the airways of the lungs, occurring either as solitary cells or in small clusters. These cells are involved in regulating airflow and blood flow within the lungs, and they may also play a role in detecting oxygen levels. Their signaling peptides can influence local epithelial cell growth and nerve terminals.
The pancreas also contains neuroendocrine cells that manage blood sugar levels. These cells produce and release hormones like insulin and glucagon. Insulin helps lower blood sugar by facilitating glucose uptake into cells, while glucagon raises blood sugar by prompting the liver to release stored glucose.
Neuroendocrine Tumors
Neuroendocrine tumors (NETs) are abnormal growths that develop from neuroendocrine cells. These tumors can arise in various parts of the body where neuroendocrine cells are found, including the gastrointestinal tract, lungs, and pancreas. While some NETs can grow slowly, others may progress more rapidly.
A key distinction among NETs is whether they are “functional” or “non-functional.” Functional tumors actively produce and release an excess of hormones, leading to specific symptoms related to that hormone’s overproduction. Non-functional tumors do not produce significant amounts of hormones, and symptoms often arise from the tumor’s size or its pressure on nearby organs.
NETs are also classified by their “grade,” which describes how much the tumor cells resemble normal neuroendocrine cells. Well-differentiated tumors have cells that look very similar to healthy neuroendocrine cells and grow more slowly. Poorly-differentiated tumors have cells that appear very different from normal cells and are more aggressive and grow quickly.
Associated Conditions and Symptoms
The symptoms associated with neuroendocrine tumors are highly varied, depending on the tumor’s location and whether it produces hormones. A NET in the lung might cause respiratory issues such as a persistent cough, shortness of breath, or wheezing. If a tumor is located in the pancreas, it could lead to problems with blood sugar regulation, such as low blood sugar (hypoglycemia) from excess insulin, or high blood sugar (hyperglycemia) from excess glucagon.
Functional tumors can cause distinct symptom complexes. Carcinoid syndrome is a well-known example, resulting from NETs, often in the gastrointestinal tract, releasing large amounts of serotonin and other vasoactive substances into the bloodstream. Hallmarks of carcinoid syndrome include sudden flushing of the skin, often on the face and neck, and persistent diarrhea. Some individuals may also experience abdominal pain, heart palpitations, or wheezing.
Diagnosis and Treatment Approaches
Diagnosing neuroendocrine tumors often involves specialized tests to detect these cells or their products. Blood and urine tests can measure levels of hormone byproducts, such as 5-hydroxyindoleacetic acid (5-HIAA) in urine, which is a breakdown product of serotonin and can indicate a functional tumor like those causing carcinoid syndrome. Imaging scans are important, with techniques like OctreoScan or Gallium-68 DOTATATE PET/CT. These scans use radioactive tracers that bind to specific receptors often found on neuroendocrine cells, helping pinpoint tumor locations.
Treatment approaches for NETs are tailored to the individual, considering factors like tumor type, location, size, and whether it has spread. Surgery is often the primary treatment if the tumor can be completely removed, aiming to excise the cancerous growth. For functional tumors, medical therapies such as somatostatin analogs (e.g., octreotide or lanreotide) are used to control the overproduction of hormones and alleviate symptoms like flushing and diarrhea. Beyond symptom management, treatments to slow tumor growth or destroy cancer cells include peptide receptor radionuclide therapy (PRRT), targeted therapies that block specific pathways involved in cancer growth, or chemotherapy, which uses drugs to kill rapidly dividing cells.