Carcinoid Tumors (Well-Differentiated Neuroendocrine Tumors), from the CureRays guide library.

Carcinoid tumors are slow-growing neuroendocrine tumors, most often in the lung or digestive tract — many are cured by surgery, and when they spread, hormone-blocking medicine and a special targeted radiation called PRRT can control them for years.

What it is.

Carcinoid tumors are a type of well-differentiated neuroendocrine tumor — growths that begin in the body's neuroendocrine cells, specialized cells scattered throughout organs that can release hormones into the bloodstream. The term 'carcinoid' is an older name still widely used for the well-behaved, slow-growing end of the neuroendocrine tumor family. They arise most often in the lungs (bronchial carcinoids) and in the digestive tract — the small intestine, appendix, rectum, and stomach. Because they grow slowly, many are found early and incidentally, for example during an appendix operation, a colonoscopy, or a scan for another reason. A distinctive feature of some carcinoid tumors is that they can make hormones; when a tumor releases enough of these substances into the blood — usually once it has spread to the liver — it can cause 'carcinoid syndrome,' with flushing of the skin, diarrhea, wheezing, and over time heart-valve problems. Many carcinoids, however, cause no hormone symptoms at all. The behavior of these tumors is generally favorable: they tend to grow slowly and, when localized, are frequently cured by surgery alone. Even when they have spread, their slow pace means people can live well for many years with treatment. Care is highly specialized and involves a team, because the right plan depends on where the tumor started, its grade (how fast its cells divide), whether it makes hormones, and whether and where it has spread. Treatments range from surgery for localized tumors to hormone-blocking injections, liver-directed therapies, and a targeted form of radiation called peptide receptor radionuclide therapy (PRRT) for tumors that have spread.

How radiation treats it.

Radiation plays a distinctive and powerful role in carcinoid and other well-differentiated neuroendocrine tumors, and it works differently from the external-beam radiation used for many cancers. The signature treatment is peptide receptor radionuclide therapy, or PRRT. Most carcinoid tumors carry large numbers of a specific docking site on their surface called the somatostatin receptor. PRRT takes advantage of this: a small molecule that fits that receptor is joined to a radioactive atom (lutetium-177) and given as an intravenous infusion. The molecule circulates through the bloodstream and latches onto the tumor cells wherever they are in the body, and the attached radioactive atom then delivers its energy at very short range, damaging the DNA of the tumor cells from the inside while largely sparing surrounding healthy tissue. This is an example of a 'theranostic' approach — the very same receptor-targeting that is used to light the tumor up on a DOTATATE PET scan is used to deliver the treatment, so doctors can confirm in advance that a tumor is likely to respond. PRRT is especially valuable because carcinoids that have spread are often scattered in many places, where surgery and external-beam radiation cannot reach everything; an infused, tumor-seeking radiation can treat all those deposits at once. For liver metastases specifically, another internal radiation option delivers tiny radioactive beads through the liver's blood vessels, lodging them in the tumors. External-beam radiation, including precise stereotactic body radiation, still has a role for controlling specific problem areas — a painful bone deposit or a tumor pressing on something important. Because these tumors grow slowly, radiation is typically used to achieve durable, long-term control, often keeping advanced disease stable for years while preserving quality of life.

The ways we can treat it.

Peptide receptor radionuclide therapy (PRRT). A radioactive atom (lutetium-177) is attached to a molecule that locks onto somatostatin receptors on neuroendocrine tumor cells; given as an intravenous infusion, it travels through the body and delivers radiation directly to tumor cells wherever they are, sparing most normal tissue.

Theranostic pairing (scan then treat). A DOTATATE PET scan first confirms that the tumor cells carry the receptors PRRT targets; the same targeting principle used to image the tumor is then used to treat it, so therapy is matched to tumors most likely to respond.

External-beam radiation for specific sites. Focused external-beam radiation, including stereotactic body radiation (SBRT), can control individual problem spots — such as a painful bone metastasis or a tumor pressing on a structure — even though it is not the main treatment for widespread disease.

Selective internal radiation (radioembolization). For liver metastases, tiny radioactive beads delivered through the liver's blood vessels lodge in the tumors and irradiate them from within while sparing much of the healthy liver.

Questions we hear often.

Is a carcinoid tumor cancer? Yes, but usually a slow-growing kind. Carcinoid tumors are well-differentiated neuroendocrine tumors, which tend to grow much more slowly than most cancers. Many localized ones are cured by surgery, and even when they spread, their slow pace means people often live well for many years with treatment. A smaller number behave more aggressively, which is why grade — how fast the cells divide — is assessed alongside stage.

What is PRRT, and how is it different from regular radiation? PRRT (peptide receptor radionuclide therapy) is a targeted radiation given as an infusion rather than aimed from a machine. A tumor-seeking molecule carries a radioactive atom through the bloodstream and attaches to neuroendocrine tumor cells wherever they are, delivering radiation from the inside. This lets it treat tumors scattered in many places at once — something external-beam radiation, which targets one area, cannot do.

What is carcinoid syndrome? Carcinoid syndrome happens when a tumor releases hormone-like substances into the blood, usually after it has spread to the liver. It causes flushing of the skin, diarrhea, and sometimes wheezing, and over time can affect the heart valves. Long-acting somatostatin-analog injections control these symptoms well and also help slow the tumor, which is why they are a cornerstone of treatment for hormone-producing tumors.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.