In most cases, gastrointestinal carcinoid tumors may not produce symptoms in their early stages. However, they may sometimes cause mild abdominal pain if the tumors cause a bending or blockage of the intestines. But this pain does not typically cause a person to seek medical help.

Usually, symptoms do not appear until the tumor has reached a more advanced stage. After it has spread, a patient may experience periodic abdominal pain or rarely gastrointestinal bleeding.

Some carcinoid tumors also produce excessive levels of adrenocorticotrophic hormone (ACTH), which stimulates the adrenal glands to secrete excessive levels of cortisol and other hormones. This can result in the following symptoms:

• Weight gain
  
• Weakness
  
• Increased body and facial hair

Carcinoid syndrome occurs in about 10 percent of cases, according to the American Cancer Society. It may indicate that the cancer has spread to the liver, which usually breaks down substances released by the carcinoid tumors. Symptoms of this syndrome may include:

• Facial flushing or feeling of warmth in the face and neck
  
• Wheezing
  
• Diarrhea
  
• Rapid pulse
  
• Severe drop in blood pressure
  
• Small, benign skin tumors (angiomas)

Many patients find that these symptoms worsen during periods of stress, strenuous exercise or alcohol consumption. If substances secreted by the tumor are allowed to build up in the body over long periods of time, they may damage the heart valves.