Your body’s cells communicate with each other through hormones. Cells and glands located throughout the body produce hormones. These hormones control functions like metabolism, appetite, and even your emotions. The system in your body that produces hormones is known as the endocrine system.

Some nerve cells communicate with chemicals, too. Those are called neuro (for nerve) endocrine cells.

When a cell grows abnormally, it forms a tumor. Tumors are classified as cancer when they can spread within an organ or to other organs. In the neuroendocrine system, the cancer is called a neuroendocrine tumor, or NET. When hormone-producing NETs spread to the liver, they can cause symptoms that can make daily life difficult. In fact, carcinoid syndrome doesn't necessarily mean your tumor is getting worse. In some cases, patients with carcinoid syndrome have stable disease.