A tumor begins when normal cells in the body become abnormal and grow uncontrollably, forming a mass. A tumor can be benign or malignant. A benign tumor is not cancerous and usually can be removed without it causing much harm. A malignant tumor is cancerous, meaning it can spread to and damage the body's healthy tissues if it is not found early and treated.
About the endocrine system
The endocrine system is made up of cells that make hormones. Hormones are chemical substances that are made in the body and carried in the bloodstream to have a specific regulatory effect on the activity of other organs or cells in the body. For example, a component of the pancreas is made up of specialized cells clustered together in islands within the organ, called islets of Langerhans. These cells make multiple hormonesâthe most important being insulin, which is a substance that helps control the amount of sugar in the blood.
Part of the endocrine system is the neuroendocrine system, which is made up of cells that are a cross between traditional endocrine cells (or hormone-producing cells) and nerve cells. Neuroendocrine cells are found throughout the body in organs, such as the lungs and gastrointestinal tract, and perform specific functions, such as regulating the air and blood flow through the lungs and controlling the speed at which food is moved through the gastrointestinal tract.
About endocrine tumors
An endocrine tumor is a growth that affects the parts of the body that secrete hormones. Because an endocrine tumor starts in the cells that make hormones, the tumor itself can make hormones and cause serious illness.
There are several types of endocrine tumors. For more specific information on each type, select a name below:
- Adrenal gland tumor  (includes information on adenomas and adrenocortical carcinoma)
- Carcinoid tumors  (includes information on both lung and gastrointestinal carcinoid tumors)
- Islet cell tumor  (includes information on gastrinoma, insulinoma, glucagonoma, VIPoma, somatostatinoma, and nonfunctioning tumors)
- Neuroendocrine tumor  (includes information on Merkel cell cancer, pheochromocytoma, and neuroendocrine carcinoma)
- Parathyroid tumor 
- Pituitary gland tumor 
- Thyroid cancer 
Find out more about basic terms used in this section .