A neuroendocrine tumor is a type of growth that starts in specialized neuroendocrine cells. These cells have features of both nerve cells and hormone-producing cells. Neuroendocrine cells are found throughout the body and help control many important functions by releasing hormones in response to signals from the nervous system.
Neuroendocrine tumors can develop in many different organs, but they are most commonly found in the gastrointestinal tract (such as the stomach, small intestine, appendix, and colon), the pancreas, and the lungs. They can also arise in other parts of the body, including the thyroid gland, adrenal glands, and skin.
Yes, all neuroendocrine tumors are considered malignant or cancerous because they have the potential to spread to other parts of the body. However, their behavior can be highly variable. Some grow very slowly and may not spread for many years, while others are more aggressive and can spread quickly. The grade of the tumor, which describes how fast the cancer cells are growing, plays a major role in determining how the tumor behaves.
There are different types of neuroendocrine tumors. Some are defined by their microscopic features, while others are classified based on their location in the body.
The symptoms of a neuroendocrine tumor depend on where it is located and whether it is producing hormones. Some neuroendocrine tumors do not cause any symptoms and are found during tests for other conditions. When symptoms do occur, they may include:
The exact cause of neuroendocrine tumors is usually unknown. However, some cases are linked to genetic conditions that run in families, such as multiple endocrine neoplasia type 1 (MEN1) or von Hippel-Lindau disease. Other factors, such as long-term inflammation or damage to the tissues where neuroendocrine cells are found, may also contribute to the development of these tumors.
Grading is a way for pathologists to describe how fast a tumor is likely to grow and spread. In most parts of the body, only well differentiated neuroendocrine tumors are divided into three grades:
The grade is determined by counting the number of mitotic figures (dividing cells) under the microscope or by measuring a protein called Ki-67, which shows how many cells are actively growing. The specific cutoffs used to determine G1, G2, and G3 vary slightly depending on the part of the body where the tumor is located.
Under the microscope, neuroendocrine tumors comprise small to medium-sized cells that may be arranged in clusters, nests, or ribbons. The tumor cells often have round or oval nuclei with a finely speckled pattern inside, which pathologists describe as “salt and pepper chromatin.” The cytoplasm, or body of the cell, may appear pale or pink.
Pathologists use a special test called immunohistochemistry to confirm the diagnosis of a neuroendocrine tumor. Immunohistochemistry is a technique that allows pathologists to detect specific proteins in the tumor cells by applying special stains to the tissue sample.
Typical proteins found in neuroendocrine tumors include:
If the tumor is located in the pancreas, additional tests may be performed to check for other neuroendocrine markers, such as insulin, glucagon, or somatostatin, depending on the type of tumor.
The prognosis for a person diagnosed with a neuroendocrine tumor depends on several factors, including the tumor’s location, size, grade, and whether it has spread to other parts of the body. Many neuroendocrine tumors, especially those that are low-grade (G1), grow slowly and may not cause serious problems for many years. Higher-grade tumors (G3), on the other hand, tend to grow and spread more quickly, making treatment more challenging.
With advances in diagnosis and treatment, many people with neuroendocrine tumors can live long and active lives, especially when the tumor is found early. Treatment options may include surgery, targeted therapies, and medications to control hormone-related symptoms.
North American Neuroendocrine Tumour Society