Carcinoid tumor presents many diagnostic challenges. As rare cancers go, carcinoid tumors are among the more unusual. These slow-growing tumors can occur in almost any part of the body. If there are any symptoms at all, they tend to be misdiagnosed as other diseases, and the tumors are often discovered during unrelated surgeries or medical procedures. These baffling characteristics make it difficult to prevent and diagnose carcinoid tumors, which bring a large number of patients to M. D. Anderson.

Carcinoid tumors can develop wherever there are neuroendocrine (hormone-producing) cells in the body. “About 75% of carcinoids arise in the gastrointestinal tract, particularly the small intestine,” Dr. Yao says. “Another 24% occur in the lung and the remaining 1% occur everywhere else.” They are rare, occurring in roughly two out of every 100,000 people, Dr. Yao says, although accurate statistics for carcinoid tumors are not readily available.

Many carcinoids exist without symptoms for years, which makes early diagnosis difficult at best. “Because it’s such a slow-growing cancer, there are a lot of patients with incidental carcinoids that may never be detected,” Dr. Yao says. They are generally diagnosed only when they grow large enough to cause a bowel obstruction or other discomfort. In fact, most early-stage carcinoids are discovered incidentally during colonoscopies, regular physical exams and appendectomies or other surgeries.

Larger, more advanced carcinoid tumors cause symptoms that include diarrhea, skin flushing and asthma – a combination of conditions known as carcinoid syndrome. “Patients with a long history of these symptoms were often previously thought to have sprue, irritable bowel syndrome or other diseases, and their carcinoids weren’t diagnosed until much later,” Dr. Yao says. “I have a patient who had skin flushing for 10 years, and is just now being diagnosed with a carcinoid tumor.”

The cause of carcinoid tumors is still not well understood. “There have been some studies linking carcinoids to multiple endocrine neoplasia (MEN), but that accounts for only a very small set of patients,” Dr. Yao says. “Chronic gastritis or other conditions that cause excess production of gastrin may also play a role, but there are too few studies at this point to determine what causes these tumors.”

Predicting the survival rate of carcinoid tumor patients isn’t easy, either. “There is an often-quoted retrospective review that shows a five-year survival rate of about 67% in patients with carcinoid syndrome, but good data isn’t easy to come by,” Dr. Yao says. “There are efforts under way to better define the prognosis of carcinoids and to create a uniform staging system to help predict tumor progression and patient survival.

Treatment of carcinoids depends largely on size and metastasis (spread). For small tumors that have not metastasized, surgery is the best option and often has a high success rate. “The success of shrinking carcinoids with chemotherapy is not as high as we’d like it to be; only about 10% to 15% at best,” Dr. Yao says. “Conventional radiation therapy is often difficult because carcinoids tend occur in the small bowel and other sensitive areas of the body.” Targeted internal radiation therapies are being tested at some cancer centers, and some new biologic therapies may soon be studied in clinical trials.

Dr. Yao is lead investigator on an M. D. Anderson clinical trial of the drug Gleevec for patients with metastatic or inoperable carcinoid tumors. Gleevec has been used successfully to treat certain leukemias and is being tested on other cancers. “It’s too early to tell if Gleevec will work for carcinoids, since it’s a new study,” he says. “We’re still actively recruiting patients.”

What’s the outlook for carcinoid patients? The lack of effective screening tools for the disease means that many, if not most, carcinoids won’t be diagnosed until they’re advanced, a situation that’s not likely to change soon. However, the outlook is far from grim. “We have to be careful how we define successful treatment,” Dr. Yao says. “Certainly, these patients can have good quality of life and live a long time even with their disease. While we may not have a cure for a majority of metastatic carcinoid tumors, we can still help these patients.” 

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