Overview

A tumor occurs when cells in the body become abnormal and multiply without control or order, forming a growth of tissue. 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 and can be harmful if not found early and treated. It can invade and damage the body’s healthy tissues and organs.

The endocrine system consists of cells that produce hormones. Hormones are chemical substances that are formed 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.

An endocrine tumor is a growth that affects the parts of the body that secrete hormones. Because an endocrine tumor arises from cells that produce hormones, the tumor itself can produce hormones and cause serious illness.

A carcinoid tumor starts in the hormone-producing cells of various organs, primarily the gastrointestinal tract (such as the stomach and intestines) and lungs, but also the pancreas, testicles (in males) or ovaries (in females). More than one carcinoid tumor can occur within the same organ. The cause of a carcinoid tumor is unknown.

A carcinoid tumor is classified as a neuroendocrine tumor, which means it starts in cells of the neuroendocrine system that produce hormones. A carcinoid tumor can produce high levels of neuropeptides and amines (hormone-like substances); however, they may not be released in high enough quantities to cause symptoms or these may be defective and, therefore, not produce symptoms. A carcinoid tumor can grow slowly for many years without causing symptoms. Although this tumor is malignant (cancerous), a carcinoid tumor is often referred to as "cancer in slow motion."

Here is a general overview of where carcinoid tumors begin:

• 39% occur in the small intestine
  
  
• 15% occur in the rectum
  
  
• 10% occur in the bronchial system of the lungs
  
  
• 7% occur in the appendix
  
  
• 5% to 7% occur in the colon
  
  
• 2% to 4% occur in the stomach
  
  
• 2% to 3% occur in the pancreas
  
  
• About 1% occur in the liver
  
  
• Rarely in ovaries, testicles, and other organs

Carcinoid tumors make up only 1% of cancers of the gastrointestinal tract, but make up about 50% of all small intestine cancers.

Specifically regarding the lung, there are two subtypes of lung carcinoid tumors: typical and atypical. The difference relates to how a tumor processes and makes serotonin (5-HT, a neurotransmitter involved in behavior and depression):

• A typical lung carcinoid tumor has a high blood concentration of serotonin, chromogranin-A, and high urine levels of 5-HIAA (a product of serotonin breakdown).

• An atypical lung carcinoid tumor has a normal blood concentration of serotonin, chromogranin-A, and normal urine levels of 5-HIAA, but a high urine concentration of serotonin and 5-HTP (an amino acid) and can produce 5-HTP.

Statistics

It is estimated that 11,000 to 12,000 people are diagnosed with a carcinoid tumor each year in the United States. The number of carcinoid tumors diagnosed has been increasing, but the reason for this is unknown.

About two-thirds of all carcinoid tumors occur in the gastrointestinal tract. The overall relative survival rate (the percentage of people who survive after the cancer is detected, excluding those who die from other diseases) for people with gastrointestinal carcinoid tumors (tumors that have not spread) is 67%.

Each year, an estimated 3,000 adults in the United States are diagnosed with lung carcinoid tumors. The five-year relative survival rate of people with typical lung carcinoid tumors is 85% to 90%. Those diagnosed with atypical lung carcinoid tumors have a five-year relative survival rate of 50% to 60%.

Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States and may not apply to a single person. It is not possible to tell a person how long he or she will live with carcinoid tumors. Because survival statistics are measured in five-year intervals, they may not represent advances made in the treatment or diagnosis of this cancer.

Source: American Cancer Society.

Find out more about basic cancer terms used in this section.