Carcinoid tumors are typically cancerous. These slow-growing tumors are often found in the gut or the lungs years after they first develop. They can spread to other parts of the body.

Carcinoid tumors are known for their slow growth rate. They often grow so slowly that treatment is unnecessary. But that doesn’t mean that carcinoid tumors are benign (noncancerous).

There’s a difference between slow-growing tumors and benign tumors. Carcinoid tumors are usually cancerous.

Carcinoid tumors are rare neuroendocrine tumors that primarily occur in the gastrointestinal (GI) tract and lungs. While some can remain localized and not spread to other parts of the body, others can metastasize (spread) and require urgent treatment.

Carcinoid tumors often grow slowly for many years without causing any symptoms.

Read on for an overview of carcinoid tumors, their symptoms, and whether they’re harmless or dangerous.

Carcinoid tumors can be cancerous or noncancerous. They can become malignant (cancerous) and metastasize over time. When this happens, the cancer typically spreads first to nearby lymph nodes and then to other organs, like the liver.

Small malignant carcinoid tumors are easier to treat, as they can often be completely removed during surgery. Tumors that have metastasized are more serious and sometimes require more aggressive treatments like surgical procedures, radiation therapy, or chemotherapy.

The risk of metastasis can vary between 10–70% and depends on the tumor size.

According to several endocrinologists:

  • Only about 15% of tumors smaller than 0.4 inches (1 centimeter) in diameter spread to distant tissues.
  • About 95% of carcinoid tumors larger than 0.8 inches (2 centimeters) have already spread at the time of diagnosis.
  • It typically takes around 9 years for a carcinoid tumor to spread, cause symptoms, and lead to diagnosis.

Benign vs. malignant

Benign tumors are noncancerous. They stay in their original location, do not spread, and grow very slowly.

Malignant tumors are cancerous. They grow quickly, have irregular borders, and invade neighboring tissues. They spread to other parts of the body via the blood and lymph nodes, which is a process called metastasis.

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Carcinoid tumors usually require treatment because, by the time they are discovered, they’re usually causing symptoms, having grown larger or spread over time. But some carcinoid tumors are discovered incidentally during other tests or procedures.

If your tumor is small and slow growing, your doctor might recommend closely watching it instead of treating it. This approach, called watchful waiting, means keeping a close eye on your health with regular check-ups to see if the tumor grows or causes problems.

However, if your carcinoid tumor starts growing or causing symptoms, you will need treatment.

Treatment options include:

  • surgery to remove the tumor and nearby tissues
  • radiation therapy
  • targeted therapy
  • hormone-related drugs, such as octreotide
  • chemotherapy

Carcinoid tumors begin to cause symptoms when they grow larger or when they start producing hormones. Because carcinoid tumors are neuroendocrine tumors, the hormone-producing endocrine cells can begin releasing hormones into your bloodstream.

Symptoms of a carcinoid tumor depend on the tumor’s location, its size, which hormone it’s producing (if any), and whether it’s spread to other organs or tissues.

Tumors in your digestive tract

The most common symptom of carcinoid tumors in the gut is chronic (long lasting) diarrhea. Facial flushing is another very common symptom.

Other symptoms include:

Tumors in your lungs

Symptoms include:

Carcinoid syndrome

A group of symptoms called carcinoid syndrome can occur when a carcinoid tumor, no matter where it is, releases hormones into your bloodstream.

It is rare, but symptoms include:

Other symptoms

Some carcinoid tumors may produce hormones that affect your stomach bile or cortisol levels. If this happens, you may also experience one or more of the following symptoms:

The prognosis of carcinoid tumors is generally very good and better than other cancers affecting the gut.

According to the American Cancer Society, 89% of people with carcinoid tumors in the lung survive their cancer for over 5 years. And 94% of people with carcinoid tumors in the gastrointestinal tract survive for at least 5 years.

Your specific outlook will depend on a number of factors, such as:

  • the size of the tumor
  • the location of the tumor
  • the success of the surgical extraction
  • where the cancer has spread
  • your overall health

If your carcinoid tumor is small and slow-growing, healthcare professionals might suggest a strategy of watchful waiting. This means regular monitoring of the tumor without treatment.

Your commitment to regular monitoring will also be important to your prognosis.

Carcinoid tumors are slow-growing neuroendocrine tumors found in the gastrointestinal tract and lungs. While some remain benign, others become malignant (cancerous).

Benign tumors are monitored closely unless they cause discomfort or are too close to critical organs.