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thyroid-cancer

Thyroid Cancer

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What is thyroid cancer?

Thyroid cancer is a cancer that starts in the thyroid gland. To understand thyroid cancer, it helps to know about the normal structure and function of the thyroid gland.

 

The thyroid gland

The thyroid gland is below the thyroid cartilage (Adam’s apple) in the front part of the neck. In most people, the thyroid cannot be seen or felt. It is butterfly shaped, with 2 lobes — the right lobe and the left lobe — joined by a narrow isthmus (see picture).

The thyroid gland has 2 main types of cells:

Follicular cells use iodine from the blood to make thyroid hormone, which helps regulate a person’s metabolism. Having too much thyroid hormone (a condition called hyperthyroidism) can cause a rapid or irregular heartbeat,

trouble sleeping, nervousness, hunger, weight loss, and a feeling of being too warm. Having too little hormone (called hypothyroidism) causes a person to slow down, feel tired, and gain weight. The amount of thyroid hormone released by the thyroid is regulated by the pituitary gland at the base of the brain, which makes a substance calledthyroid-stimulating hormone (TSH).

C cells (also called parafollicular cells) make calcitonin, a hormone that helps control how the body uses calcium.

Other, less common cells in the thyroid gland include immune system cells (lymphocytes) and supportive (stromal) cells.

Different cancers develop from each kind of cell. The differences are important because they affect how serious the cancer is and what type of treatment is needed.

Many types of growths and tumors can develop in the thyroid gland. Most of these are benign (non-cancerous) but others are malignant (cancerous), which means they can spread into nearby tissues and to other parts of the body.

Benign thyroid enlargement and nodules

Changes in the thyroid gland’s size and shape can often be felt or even seen by patients or by their doctor.

The medical term for an abnormally large thyroid gland is goiter. Some goiters are diffuse, meaning that the whole gland is large. Other goiters are nodular, meaning that the gland is large and has one or more nodules (bumps) in it. There are many reasons the thyroid gland might be larger than usual, and most of the time it is not cancer. Both diffuse and nodular goiters are usually caused by an imbalance in certain hormones. For example, not getting enough iodine in the diet can cause changes in hormone levels and lead to a goiter.

Lumps or bumps in the thyroid gland are called thyroid nodules. Most thyroid nodules are benign, but about 1 in 20 is cancerous. Sometimes these nodules make too much thyroid hormone and cause hyperthyroidism.

People can develop thyroid nodules at any age, but they occur most commonly in older adults. Fewer than 1 in 10 adults have thyroid nodules that can be felt by a doctor. But when the thyroid is looked at using ultrasound, many more people are found to have nodules that are too small to feel.

Most nodules are cysts filled with fluid or with a stored form of thyroid hormone called colloid.

Solid nodules have little fluid or colloid. These nodules are more likely to be cancerous than are fluid-filled nodules. Still, most solid nodules are not cancer. Some types of solid nodules, such as hyperplastic nodules and adenomas, have too many cells, but the cells are not cancer cells.

Benign thyroid nodules sometimes can be left alone (not treated) as long as they’re not growing or causing symptoms. Others may require some form of treatment.

Malignant (cancerous) thyroid tumors

There are several types of thyroid cancer.

Differentiated thyroid cancers

Most thyroid cancers are differentiated cancers. In these cancers, the cells look a lot like normal thyroid tissue when seen under a microscope. These cancers develop from thyroid follicular cells.

Papillary carcinoma: About 8 of 10 thyroid cancers are papillary carcinomas (also called papillary cancers orpapillary adenocarcinomas). Papillary carcinomas tend to grow very slowly and usually develop in only one lobe of the thyroid gland. Even though they grow slowly, papillary carcinomas often spread to the lymph nodes in the neck. Still, these cancers can often be treated successfully and are rarely fatal.

There are several subtypes of papillary carcinoma. Of these, the follicular subtype (also called mixed papillary-follicular variant) occurs most often. The usual form of papillary carcinoma and the follicular subtype have the same good outlook (prognosis) when found early, and they are treated the same way. Other subtypes of papillary carcinoma (columnar, tall cell, and diffuse sclerosing) are not as common and tend to grow and spread more quickly.

Follicular carcinoma: Follicular carcinoma, also called follicular cancer or follicular adenocarcinoma, is the next most common type, making up about 1 out of 10 thyroid cancers. It is more common in countries where people don’t get enough iodine in their diet. These cancers usually do not spread to lymph nodes, but they can spread to other parts of the body, such as the lungs or bones. The prognosis (outlook) for follicular carcinoma is not quite as good as that of papillary carcinoma, although it is still very good in most cases.

Hürthle cell carcinoma, also known as oxyphil cell carcinoma, is actually a variant of follicular carcinoma. It accounts for about 3% of thyroid cancers. The prognosis may not be as good as that of typical follicular carcinoma because this type is harder to find and treat. This is because it is less likely to absorb radioactive iodine, which is used both for treatment and to look for the spread of differentiated thyroid cancer.

Other types of thyroid cancers

These thyroid cancers occur less often than differentiated thyroid cancers.

Medullary thyroid carcinoma: Medullary thyroid carcinoma (MTC) accounts for about 4% of thyroid cancers. It develops from the C cells of the thyroid gland, which normally make calcitonin, a hormone that helps control the amount of calcium in blood. Sometimes this cancer can spread to lymph nodes, the lungs, or liver even before a thyroid nodule is discovered.

Medullary thyroid cancers often release too much calcitonin and a protein called carcinoembryonic antigen (CEA) into the blood. These substances can be detected with blood tests.

Because MTC does not absorb or take up radioactive iodine (used for treatment and to find metastases of differentiated thyroid cancer), the prognosis (outlook) is not quite as good as that for differentiated thyroid cancers. There are 2 types of MTC:

Sporadic MTC, which accounts for about 8 of 10 cases, is not inherited. That is, it does not run in families. It occurs mostly in older adults and affects only one thyroid lobe.

Familial MTC is inherited and can occur in each generation of a family. These cancers often develop during childhood or early adulthood and can spread early. Patients usually have cancer in several areas of both lobes. Familial MTC is often linked with an increased risk of other types of tumors. This is described in more detail in the section “What are the risk factors for thyroid cancer?”

Anaplastic carcinoma: Anaplastic carcinoma (also called undifferentiated carcinoma) is a rare form of thyroid cancer, making up about 2% of all thyroid cancers. It is thought to sometimes develop from an existing papillary or follicular cancer. This cancer is called undifferentiated because the cancer cells do not look very much like normal thyroid cells under the microscope. This cancer often spreads quickly into the neck and to other parts of the body, and is very hard to treat.

Thyroid lymphoma: Lymphoma is very uncommon in the thyroid gland. Lymphomas are cancers that develop from lymphocytes, the main cell type of the immune system. Most lymphocytes are found in lymph nodes, which are pea-sized collections of immune cells scattered throughout the body (including the thyroid gland). Lymphomas are discussed in the separate American Cancer Society document, Non-Hodgkin Lymphoma.

Thyroid sarcoma: These rare cancers start in the supporting cells of the thyroid. They are often aggressive and hard to treat. Sarcomas are discussed in the separate American Cancer Society document, Sarcoma: Adult Soft Tissue Cancer.

Parathyroid cancer

Behind, but attached to, the thyroid gland are 4 tiny glands called the parathyroids. The parathyroid glands help regulate the body’s calcium levels. Cancers of the parathyroid glands are very rare — there are probably fewer than 100 cases each year in the United States.

Parathyroid cancers are often found because they cause high blood calcium levels. This makes a person tired, weak, and drowsy. It can also makes you urinate (pee) a lot, causing dehydration, which can make the weakness and drowsiness worse. Other symptoms include bone pain and fractures, pain from kidney stones, depression, and constipation.

Larger parathyroid cancers may also be found as a nodule near the thyroid. No matter how large the nodule is, the only treatment is to remove it surgically. Unfortunately, parathyroid cancer is much harder to cure than thyroid cancer.

The remainder of this document only discusses thyroid cancer.

What are the risk factors for thyroid cancer?

A risk factor is anything that affects a person’s chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be changed. Others, like a person’s age or family history, can’t be changed.

But risk factors don’t tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may have few or no known risk factors. Even if a person with thyroid cancer has a risk factor, it is very hard to know how much that risk factor may have contributed to the cancer.

Scientists have found a few risk factors that make a person more likely to develop thyroid cancer.

Gender and age : For unclear reasons thyroid cancers (like almost all diseases of the thyroid) occur about 3 times more often in women than in men.

Thyroid cancer can occur at any age, but the risk peaks earlier for women (who are most often in their 40s or 50s when diagnosed) than for men (who are usually in their 60s or 70s).

A diet low in iodine : Follicular thyroid cancers are more common in areas of the world where people’s diets are low in iodine. In the United States, most people get enough iodine in their diet because it is added to table salt and other foods. A diet low in iodine may also increase the risk of papillary cancer if the person also is exposed to radioactivity.

Radiation : Exposure to radiation is a proven risk factor for thyroid cancer. Sources of such radiation include certain medical treatments and radiation fallout from power plant accidents or nuclear weapons.

Having had head or neck radiation treatments in childhood is a risk factor for thyroid cancer. Risk depends on how much radiation is given and the age of the child. In general, the risk increases with larger doses and with younger age at treatment. Before the 1960s, children were sometimes treated with low doses of radiation for things we wouldn’t use radiation for now, like acne, fungus infections of the scalp (ringworm), or enlarged tonsils or adenoids. Years later, the people who had these treatments were found to have a higher risk of thyroid cancer. Radiation therapy in childhood for some cancers such as lymphoma, Wilms tumor, and neuroblastoma also increases risk. Thyroid cancers that develop after radiation therapy are not more serious than other thyroid cancers.

Imaging tests such as x-rays and CT scans also expose children to radiation, but at much lower doses, so it’s not clear how much they might raise the risk of thyroid cancer (or other cancers). If there is an increased risk it is likely to be small, but to be safe, children should not have these tests unless they are absolutely needed. When they are needed, they should be done using the lowest dose of radiation that still provides a clear picture.

Several studies have pointed to an increased risk of thyroid cancer in children because of radioactive fallout from nuclear weapons or power plant accidents. For instance, thyroid cancer was many times more common than normal in children who lived near Chernobyl, the site of a 1986 nuclear plant accident that exposed millions of people to radioactivity. Adults involved with the cleanup after the accident and those who lived near the plant have also had higher rates of thyroid cancer. Children who had more iodine in their diet appeared to have a lower risk.

Some radioactive fallout occurred over certain regions of the United States after nuclear weapons were tested in western states during the 1950s. This exposure was much, much lower than that around Chernobyl. A higher risk of thyroid cancer has not been proven at these low exposure levels. If you are concerned about possible exposure to radioactive fallout, discuss this with your doctor.

Being exposed to radiation when you are an adult carries much less risk of thyroid cancer.

Hereditary conditions and family history

Several inherited conditions have been linked to different types of thyroid cancer, as has family history. Still, most people who develop thyroid cancer do not have an inherited condition or a family history of the disease.

Medullary thyroid cancer

About 1 out of 3 medullary thyroid carcinomas (MTCs) result from inheriting an abnormal gene. These cases are known as familial medullary thyroid carcinoma (FMTC). FMTC can occur alone, or it can be seen along with other tumors.

The combination of FMTC and tumors of other endocrine glands is called multiple endocrine neoplasia type 2 (MEN 2). There are 2 subtypes, MEN 2a and MEN 2b, both of which are caused by mutations (defects) in a gene called RET.

In MEN 2a, MTC occurs along with pheochromocytomas (tumors that make adrenaline) and with parathyroid gland tumors.

In MEN 2b, MTC is associated with pheochromocytomas and with benign growths of nerve tissue on the tongue and elsewhere called neuromas. This subtype is much less common than MEN 2a.

In these inherited forms of MTC, the cancers often develop during childhood or early adulthood and can spread early. MTC is most aggressive in the MEN 2b syndrome. If MEN 2a, MEN 2b, or isolated FMTC runs in your family, you may be at very high risk of developing MTC. Ask your doctor about having regular blood tests or ultrasound exams to look for problems and the possibility of genetic testing.

Other thyroid cancers

People with certain inherited medical conditions have a higher risk of more common forms of thyroid cancer. Higher rates of thyroid cancer occur among people with uncommon genetic conditions such as:

Familial adenomatous polyposis (FAP): People with this syndrome develop many colon polyps and have a very high risk of colon cancer. They also have an increased risk of some other cancers, including papillary thyroid cancer.Gardner syndrome is a subtype of FAP in which patients also get certain benign tumors. Both Gardner syndrome and FAP are caused by defects in the gene APC.

Cowden disease: People with this syndrome have an increased risk of thyroid, endometrial (uterine), and breast cancers. The thyroid cancers tend to be either the papillary or follicular type. This syndrome is caused by defects in the gene PTEN.

Carney complex, type I: People with this syndrome may develop a number of benign tumors and hormone problems. They also have an increased risk of papillary and follicular thyroid cancers. This syndrome is caused by defects in the gene PRKAR1A.

If you suspect you might have a familial condition, talk with your doctor, who might recommend genetic counseling if your medical history warrants it.

Papillary and follicular thyroid cancers do seem to run in some families. Having a first-degree relative (parent, brother, sister, or child) with thyroid cancer, even without a known inherited syndrome in the family, increases your risk of thyroid cancer. The genetic basis for these cancers is not totally clear.

Do we know what causes thyroid cancer?

Thyroid cancer is linked with a number of inherited conditions, but the exact cause of most thyroid cancers is not yet known.

Certain changes in a person’s DNA can cause thyroid cells to become cancerous. DNA is the chemical in each of our cells that makes up our genes – the instructions for how our cells function. We usually look like our parents because they are the source of our DNA. But DNA affects more than just how we look. It also can influence our risk for developing certain diseases, including some kinds of cancer.

Some genes contain instructions for controlling when our cells grow and divide into new cells. Certain genes that help cells grow and divide or make them live longer than they should are called oncogenes. Other genes that slow down cell division or make cells die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes.

People inherit 2 copies of each gene – one from each parent. We can inherit damaged DNA from one or both parents. Most cancers, though, are not caused by inherited gene changes. In these cases, the genes change during a person’s life. They may occur when a cell’s DNA is damaged by something in the environment, like radiation, or they may just be random events that sometimes happen inside a cell, without an outside cause.

Papillary thyroid cancer

Several DNA mutations (changes) have been found in papillary thyroid cancer. Many of these cancers have changes in specific parts of the RET gene. The altered form of this gene, known as the PTC oncogene, is found in about 10% to 30% of papillary thyroid cancers overall, and in a larger percentage of these cancers in children and/or linked with radiation exposure. These RET mutations usually are acquired during a person’s lifetime rather than being inherited. They are found only in cancer cells and are not passed on to the patient’s children.

Many papillary thyroid cancers have a mutated BRAF gene. The BRAF mutation is less common in thyroid cancers in children and in those thought to develop from exposure to radiation. Cancers with BRAF changes tend to grow and spread to other parts of the body more quickly.

Both BRAF and RET/PTC changes are thought to make cells grow and divide. It is extremely rare for papillary cancers to have changes in both the BRAF and RET/PTC genes. Some doctors now advise testing thyroid biopsy samples for these gene mutations, as they can help diagnose cancer and may also affect the patient’s outlook.

Changes in other genes have also been tied to papillary thyroid cancer, including those in the NTRK1 gene and theMET gene.

Follicular thyroid cancer

Acquired changes in the RAS oncogene have a role in causing some follicular thyroid cancers.

Anaplastic thyroid cancer

These cancers tend to have some of the mutations described above and often have changes in the TP53 tumor suppressor gene and the CTNNB1 oncogene as well.

Medullary thyroid cancer

People who have medullary thyroid carcinoma (MTC) have mutations in different parts of the RET gene compared with papillary carcinoma patients. Nearly all patients with the inherited form of MTC and about 1 of every 10 with the sporadic (non-inherited) form of MTC have a mutation in the RET gene. Most patients with sporadic MTC have gene mutations only in their cancer cells. Those with familial MTC and MEN 2 inherit the RET mutation from a parent. These mutations are in every cell of the patient’s body and can be detected by testing the DNA of blood cells.

In people with inherited mutations of RET, one RET gene is usually normal and one is mutated. Because every person has 2 RET genes but passes only one of them to a child (the child’s other RET gene comes from the other parent), the odds that a person with familial MTC will pass a mutated gene on to a child are 1 in 2 (or 50%).

Can thyroid cancer be prevented?

Most people with thyroid cancer have no known risk factors, so it is not possible to prevent most cases of this disease.

Radiation exposure, especially in childhood, is a known risk factor for thyroid cancer. Because of this, doctors no longer use radiation to treat less serious diseases. Imaging tests such as x-rays and CT scans also expose children to radiation, but at much lower doses, so it’s not clear how much they might raise the risk of thyroid cancer (or other cancers). If there is an increased risk it is likely to be small, but to be safe, children should not have these tests unless they are absolutely needed. When they are needed, they should be done using the lowest dose of radiation that still provides a clear picture.

Blood tests can be done to look for the gene mutations found in familial medullary thyroid cancer (MTC). Because of this, most of the familial cases of MTC can be prevented or treated early by removing the thyroid gland. Once the disease is discovered in a family, the rest of the family members can be tested for the mutated gene.

If you have a family history of MTC, it is important that you see a doctor who is familiar with the latest advances in genetic counseling and genetic testing for this disease. Removing the thyroid gland in children who carry the abnormal gene will probably prevent a cancer that might otherwise be fatal.

Can thyroid cancer be found early?

Many cases of thyroid cancer can be found early. In fact, most thyroid cancers are now found much earlier than in the past and can be treated successfully.

Most early thyroid cancers are found when patients see their doctors because of neck lumps or nodules they noticed. If you have unusual symptoms such as a lump or swelling in your neck, you should see your doctor right away.

Other cancers are found by health care professionals during a routine checkup. The American Cancer Society recommends that doctors do a cancer-related checkup that includes an examination of the thyroid during routine physical exams. Some doctors also recommend that people examine their own necks twice a year to look and feel for any growths or lumps.

Early thyroid cancers are also sometimes found when people have ultrasound tests for other health problems, such as narrowing of carotid arteries (which pass through the neck to supply blood to the brain) or for enlarged or overactive parathyroid glands.

Blood tests or thyroid ultrasound can often find changes in the thyroid, but these tests are not recommended as screening tests for thyroid cancer unless a person is at increased risk, such as because of a family history of thyroid cancer.

People with a family history of medullary thyroid cancer (MTC), with or without type 2 multiple endocrine neoplasia (MEN 2), might have a very high risk for developing this cancer. Most doctors recommend genetic testing for these people when they are young to see if they carry the gene changes linked to MTC. For those who may be at risk but don’t get genetic testing, blood tests can help find MTC at an early stage, when it may still be curable. Thyroid ultrasounds may also be done in high-risk people.

How is thyroid cancer diagnosed?

Thyroid cancer may be diagnosed after a person goes to a doctor because of symptoms, or it might be found during a routine physical exam or other tests. If there is a reason to suspect you might have thyroid cancer, your doctor will use one or more tests to find out. Signs and symptoms might suggest you have thyroid cancer, but you will need tests to confirm the diagnosis.

Signs and symptoms of thyroid cancer

Prompt attention to signs and symptoms is the best way to diagnose most thyroid cancers early. Thyroid cancer can cause any of the following signs or symptoms:

A lump in the neck, sometimes growing quickly

Swelling in the neck

Pain in the front of the neck, sometimes going up to the ears

Hoarseness or other voice changes that do not go away

Trouble swallowing

Trouble breathing

A constant cough that is not due to a cold

If you have any of these signs or symptoms, talk to your doctor right away. Many of these symptoms can also be caused by non-cancerous conditions or even other cancers of the neck area. Thyroid nodules are common and are usually benign. Still, if you have any of these symptoms, it’s important to see your doctor right away so the cause can be found and treated, if needed.

Medical history and physical exam : If you have any signs or symptoms that suggest you might have thyroid cancer, your health care professional will want to know your complete medical history. You will be asked questions about your possible risk factors, symptoms, and any other health problems or concerns. If someone in your family has had thyroid cancer (especially medullary thyroid cancer) or tumors called pheochromocytomas, it is important to tell your doctor, as you might be at high risk for this disease.

Your doctor will examine you to get more information about possible signs of thyroid cancer and other health problems. During the exam, the doctor will pay special attention to the size and firmness of your thyroid and any enlarged lymph nodes in your neck.

Biopsy : The actual diagnosis of thyroid cancer is made with a biopsy, in which cells from the suspicious area are removed and looked at under a microscope. However, this might not be the first test done if you have a suspicious lump in your neck. The doctor might order other tests first, such as blood tests, an ultrasound exam, or a radioiodine scan to get a better sense of whether you might have thyroid cancer. These tests are described below.

If your doctor thinks a biopsy is needed, the simplest way to find out if a thyroid lump or nodule is cancerous is with afine needle aspiration (FNA) of the thyroid nodule. This type of biopsy can usually be done in your doctor’s office or clinic.

Before the biopsy, local anesthesia (numbing medicine) may be injected into the skin over the nodule, but in most cases an anesthetic is not needed. Your doctor will place a thin, hollow needle directly into the nodule to aspirate (take out) some cells and a few drops of fluid into a syringe. The doctor usually repeats this 2 or 3 more times, taking samples from several areas of the nodule. The biopsy samples are then sent to a lab, where they are looked at under a microscope to see if the cells look cancerous or benign.

Bleeding at the biopsy site is very rare except in people with bleeding disorders. Be sure to tell your doctor if you have problems with bleeding or are taking medicines that could affect bleeding, such as aspirin or blood thinners.

This test is generally done on all thyroid nodules that are big enough to be felt. This means that they are larger than about 1 centimeter (about 1/2 inch) across. Doctors often use ultrasound to see the thyroid during the biopsy, which helps make sure they are getting samples from the right areas. This is especially helpful for smaller nodules. FNA biopsies can also be used to get samples of swollen lymph nodes in the neck to see if they contain cancer.

Sometimes an FNA biopsy will need to be repeated because the samples didn’t contain enough cells. Most FNA biopsies will show that the thyroid nodule is benign. Rarely, the biopsy may come back as benign even though cancer is present. Cancer is clearly diagnosed in only about 1 of every 20 FNA biopsies.

Sometimes the test results first come back as “suspicious” or “of undetermined significance” if FNA findings don’t show for sure if the nodule is either benign or malignant. If this happens, the doctor may order tests on the sample to see if the BRAF or RET/PTC genes are mutated (changed). Finding these changes makes thyroid cancer much more likely, and may also play a role in determining the best treatment for the cancer.

If the diagnosis is not clear after an FNA biopsy, you might need a more involved biopsy to get a better sample, particularly if the doctor has reason to think the nodule may be cancerous. This might include a core biopsy using a larger needle, a surgical “open” biopsy to remove the nodule, or a lobectomy (removal of half of the thyroid gland). Surgical biopsies and lobectomies are done in an operating room while you are under general anesthesia (in a deep sleep). A lobectomy can also be the main treatment for some early cancers, although for many cancers the rest of the thyroid will need to be removed as well (during an operation called a completion thyroidectomy).

Imaging tests: Imaging tests may be done for a number of reasons, including to help find suspicious areas that might be cancer, to learn how far cancer may have spread, and to help determine if treatment is working.

People who have or may have thyroid cancer will get one or more of these tests.

Ultrasound: Ultrasound uses sound waves to create images of parts of your body. For this test, a small, wand-like instrument called a transducer is placed on the skin in front of your thyroid gland. It gives off sound waves and picks up the echoes as they bounce off the thyroid. The echoes are converted by a computer into a black and white image on a computer screen. You are not exposed to radiation during this test.

This test can help determine if a thyroid nodule is solid or filled with fluid. (Solid nodules are more likely to be cancerous.) It can also be used to check the number and size of thyroid nodules. How a nodule looks on ultrasound can sometimes suggest if it is likely to be a cancer, but ultrasound can’t tell for sure.

For thyroid nodules that are too small to feel, this test can be used to guide a biopsy needle into the nodule to obtain a sample. Even when a nodule is large enough to feel, most doctors prefer to use ultrasound to guide the needle.

Ultrasound can also help determine if any nearby lymph nodes are enlarged because the thyroid cancer has spread. Many thyroid specialists recommend ultrasound for all patients with thyroid nodules large enough to be felt.

Radioiodine scan : Radioiodine scans can be used to help determine if someone with a lump in the neck might have thyroid cancer. They are also often used in people who have already been diagnosed with differentiated (papillary, follicular, or Hürthle cell) thyroid cancer to help show if it has spread. Because medullary thyroid cancer cells do not absorb iodine, radioiodine scans are not used for this cancer.

For this test, a small amount of radioactive iodine (called I-131) is swallowed (usually as a pill) or injected into a vein. Over time, the iodine is absorbed by the thyroid gland (or thyroid cells anywhere in the body). A special camera is used several hours later to see where the radioactivity is.

For a thyroid scan, the camera is placed in front of your neck to measure the amount of radiation in the gland. Abnormal areas of the thyroid that have less radioactivity than the surrounding tissue are called cold nodules, and areas that take up more radiation are called hot nodules. Hot nodules usually are not cancerous, but cold nodules can be benign or cancerous. Because both benign and cancerous nodules can appear cold, this test by itself can’t diagnose thyroid cancer.

After surgery for thyroid cancer, whole-body radioiodine scans are useful to look for possible spread throughout the body. These scans become even more sensitive if the entire thyroid gland has been removed by surgery because more of the radioactive iodine is picked up by any remaining thyroid cancer cells.

Radioiodine scans work best if patients have high blood levels of thyroid-stimulating hormone (TSH, or thyrotropin). For people whose thyroid has been removed, TSH levels can be increased by stopping thyroid hormone pills for a few weeks before the test. This lowers thyroid hormone levels and causes the pituitary gland to release more TSH, which in turn stimulates any thyroid cancer cells to take up the radioactive iodine. A downside of this intentional hypothyroidism is that it can cause symptoms like tiredness, depression, weight gain, sleepiness, constipation, muscle aches, and reduced concentration. Another way to raise TSH levels before a scan is to give an injectable form of thyrotropin (Thyrogen®), which does not require withholding thyroid hormone.

Because any iodine already in the body can affect this test, people are usually told not to ingest foods or medicines that contain iodine in the days before the scan.

Radioactive iodine can also be used to treat differentiated thyroid cancer, but it is given in much higher doses. This type of treatment is described in the section.

Chest x-ray: If you have been diagnosed with thyroid cancer (especially follicular thyroid cancer), a plain x-ray of your chest may be done to see if cancer has spread to your lungs.

Computed tomography (CT) scan: The CT scan is an x-ray test that produces detailed cross-sectional images of your body. It can help determine the location and size of thyroid cancers and whether they have spread to nearby areas, although ultrasound is usually the test of choice. A CT scan can also be used to look for spread into distant organs such as the lungs.

A CT scanner has been described as a large donut, with a narrow table in the middle opening. You will need to lie still on the table while the scan is being done. CT scans take longer than regular x-rays, and you might feel a bit confined by the ring while the pictures are being taken.

Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you lie on the table. A computer then combines these pictures into images of slices of the part of your body being studied. A CT scan creates more detailed images of the soft tissues in the body than a standard x-ray.

Before the test, you may be asked to drink a contrast solution or receive an IV (intravenous) line through which a different contrast dye is injected. This helps better outline structures in your body. The injection may cause some flushing (a feeling of warmth, especially in the face). Some people are allergic and get hives. Rarely, more serious reactions like trouble breathing or low blood pressure can occur. Be sure to tell the doctor if you have any allergies or have ever had a reaction to any contrast material used for x-rays.

In some cases, a CT scan can be used to guide a biopsy needle precisely into a suspected area of cancer spread. For a CT-guided needle biopsy, you remain on the CT scanning table, while the doctor advances a biopsy needle through the skin and toward the mass. CT scans are repeated until the doctor can see that the needle is within the mass. A biopsy sample is then removed and looked at under a microscope.

One problem with using CT scans for differentiated thyroid cancer is that the CT contrast dye contains iodine, which interferes with radioiodine scans. For this reason, many doctors prefer MRI scans instead of CT scans.

Magnetic resonance imaging (MRI) scan : Like CT scans, MRI scans can be used to look for cancer in the thyroid, or cancer that has spread to nearby or distant parts of the body. But ultrasound is usually the first choice for looking at the thyroid. MRI can provide very detailed images of soft tissues such as the thyroid gland. MRI scans are also very helpful in looking at the brain and spinal cord.

MRI scans use radio waves and strong magnets instead of x-rays. The energy from the radio waves is absorbed and then released in a pattern formed by the type of body tissue and by certain diseases. A computer translates the pattern into a very detailed image of parts of the body. A contrast material called gadolinium is often injected into a vein before the scan to better show details.

MRI scans take longer than CT scans – often up to an hour. You may have to lie inside a narrow tube, which can upset people with a fear of enclosed spaces. Newer, more open MRI machines can sometimes be used instead. The machine also makes buzzing and clicking noises that you may find disturbing. Some centers provide earplugs to block this noise out.

Positron emission tomography (PET) scan : For a PET scan, a radioactive substance (usually a type of sugar related to glucose, known as FDG) is injected into the blood. The amount of radioactivity used is very low. Because cancer cells in the body grow quickly, they absorb more of the sugar than normal cells. After waiting about an hour, you lie on a table in the PET scanner for about 30 minutes while a special camera creates a picture of areas of radioactivity in the body.

This test can be very useful if your thyroid cancer is one that doesn’t take up radioactive iodine. In this situation, the PET scan may be able to tell whether the cancer has spread.

PET scan images are not finely detailed like CT or MRI images, but a PET scan can look for possible areas of cancer spread in all areas of the body at once. Some newer machines are able to do both a PET and CT scan at the same time (PET/CT scan). This lets the doctor compare an abnormal area on the PET scan with its detailed appearance on the CT.

Blood tests: Blood tests alone can’t tell if a thyroid nodule is cancerous. But they can help show if the thyroid is working normally, which may help the doctor decide what other tests may be needed.

Thyroid-stimulating hormone (TSH): Tests of blood levels of thyroid-stimulating hormone (TSH or thyrotropin) may be used to check the overall activity of your thyroid gland. Levels of TSH, which is made by the pituitary gland, may be high if the thyroid is not making enough hormones. This information can be used to help choose which imaging tests (such as ultrasound or radioiodine scans) to use to look at a thyroid nodule. The TSH level is usually normal in thyroid cancer.

T3 and T4 (thyroid hormones): These are the main hormones made by the thyroid gland. Levels of these hormones may also be measured to get a sense of thyroid gland function. The T3 and T4 levels are usually normal in thyroid cancer.

Thyroglobulin: Thyroglobulin is a protein made by the thyroid gland. Measuring the thyroglobulin level in the blood can’t be used to diagnose thyroid cancer, but it can be helpful after treatment. A common way to treat thyroid cancer is to remove most of the thyroid by surgery and then use radioactive iodine to destroy any remaining thyroid cells. These treatments should lead to a very low level of thyroglobulin in the blood within several weeks. If it is not low, this might mean that there are still thyroid cancer cells in the body. If the level rises again after being low, it is a sign that the cancer could be coming back.

Calcitonin: Calcitonin is a hormone that helps control how the body uses calcium. It is made by C cells in the thyroid, the cells that can develop into medullary thyroid cancer (MTC). If MTC is suspected or if you have a family history of the disease, blood tests of calcitonin levels can help look for MTC. This test is also used to look for the possible recurrence of MTC after treatment. Because calcitonin can affect blood calcium levels, these may be checked as well.

Carcinoembryonic antigen (CEA): People with MTC often have high blood levels of a protein called carcinoembryonic antigen (CEA). Tests for CEA can sometimes help find this cancer.

Other blood tests : You might have other blood tests as well. For example, if you are scheduled for surgery, tests will be done to check your blood cell counts, to look for bleeding disorders, and to check your liver and kidney function.

Other tests

Vocal cord exam (laryngoscopy) : Thyroid tumors can sometimes affect the vocal cords. If you are going to have surgery to treat thyroid cancer, a procedure called a laryngoscopy will probably be done first to see if the vocal cords are moving normally. For this exam, the doctor looks down the throat at the larynx (voice box) with special mirrors or with a laryngoscope, a thin tube with a light and a lens on the end for viewing.

How is thyroid cancer staged?

Staging is the process of finding out if and how far a cancer has spread. The stage of a cancer is one of the most important factors in choosing treatment options and predicting your chance for cure.

Staging is based on the results of the physical exam, biopsy, and imaging tests (ultrasound, radioiodine scan, CT scan, MRI, chest x-ray, and/or PET scans), which are described in the section, “How is thyroid cancer diagnosed?”

The TNM staging system

A staging system is a standard way to sum up how large a cancer is and how far it has spread.

The most common system used to describe the stages of thyroid cancer is the American Joint Committee on Cancer (AJCC) TNM system. The TNM system is based on 3 key pieces of information:

T indicates the size of the main (primary) tumor and whether it has grown into nearby areas.

N describes the extent of spread to nearby (regional) lymph nodes. Lymph nodes are bean-shaped collections of immune system cells to which cancers often spread first. Cells from thyroid cancers can travel to lymph nodes in the neck and chest areas.

M indicates whether the cancer has spread (metastasized) to other organs of the body. (The most common sites of spread of thyroid cancer are the lungs, the liver, and bones.)

Numbers or letters appear after T, N, and M to provide more details about each of these factors. The numbers 0 through 4 indicate increasing severity. The letter X means a category can’t be assessed because the information is not available.

T categories for thyroid cancer (other than anaplastic thyroid cancer)

TX: Primary tumor cannot be assessed.

T0: No evidence of primary tumor.

T1: The tumor is 2 cm (slightly less than an inch) across or smaller and has not grown out of the thyroid.

T1a: The tumor is 1 cm (less than half an inch) across or smaller and has not grown outside the thyroid.

T1b: The tumor is larger than 1 cm but not larger than 2 cm across and has not grown outside of the thyroid.

T2: The tumor is more than 2 cm but not larger than 4 cm (slightly less than 2 inches) across and has not grown out of the thyroid.

T3: The tumor is larger than 4 cm across, or it has just begun to grow into nearby tissues outside the thyroid.

T4a: The tumor is any size and has grown extensively beyond the thyroid gland into nearby tissues of the neck, such as the larynx (voice box), trachea (windpipe), esophagus (tube connecting the throat to the stomach), or the nerve to the larynx. This is also called moderately advanced disease.

T4b: The tumor is any size and has grown either back toward the spine or into nearby large blood vessels. This is also called very advanced disease.

T categories for anaplastic thyroid cancer

All anaplastic thyroid cancers are considered T4 tumors at the time of diagnosis.

T4a: The tumor is still within the thyroid.

T4b: The tumor has grown outside the thyroid.

N categories for thyroid cancer

NX: Regional (nearby) lymph nodes cannot be assessed.

N0: The cancer has not spread to nearby lymph nodes.

N1: The cancer has spread to nearby lymph nodes.

N1a: The cancer has spread to lymph nodes around the thyroid in the neck (called pretracheal, paratracheal, andprelaryngeal lymph nodes).

N1b: The cancer has spread to other lymph nodes in the neck (called cervical) or to lymph nodes behind the throat (retropharyngeal) or in the upper chest (superior mediastinal).

M categories for thyroid cancer

M0: There is no distant metastasis.

M1: The cancer has spread to other parts of the body, such as distant lymph nodes, internal organs, bones, etc.

Stage grouping

Once the values for T, N, and M are determined, they are combined into stages, expressed as a Roman numeral from I through IV. Sometimes letters are used to further divide a stage. Unlike most other cancers, thyroid cancers are grouped into stages in a way that also considers the subtype of cancer and the patient’s age.

Papillary or follicular (differentiated) thyroid cancer in patients younger than 45

Younger people have a low likelihood of dying from differentiated (papillary or follicular) thyroid cancer. The TNM stage groupings for these cancers take this fact into account. So, all people younger than 45 years with these cancers arestage I if they have no distant spread and stage II if they have distant spread.

Stage I (any T, any N, M0): The tumor can be any size (any T) and may or may not have spread to nearby lymph nodes (any N). It has not spread to distant sites (M0).

Stage II (any T, any N, M1): The tumor can be any size (any T) and may or may not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

Papillary or follicular (differentiated) thyroid cancer in patients 45 years and older

Stage I (T1, N0, M0): The tumor is 2 cm or less across and has not grown outside the thyroid (T1). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage II (T2, N0, M0): The tumor is more than 2 cm but not larger than 4 cm across and has not grown outside the thyroid (T2). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage III: One of the following applies:

T3, N0, M0: The tumor is larger than 4 cm across or has grown slightly outside the thyroid (T3), but it has not spread to nearby lymph nodes (N0) or distant sites (M0).

T1 to T3, N1a, M0: The tumor is any size and may have grown slightly outside the thyroid (T1 to T3). It has spread to lymph nodes around the thyroid in the neck (N1a) but not to other lymph nodes or to distant sites (M0).

Stage IVA: One of the following applies:

T4a, any N, M0: The tumor is any size and has grown beyond the thyroid gland and into nearby tissues of the neck (T4a). It might or might not have spread to nearby lymph nodes (any N). It has not spread to distant sites (M0).

T1 to T3, N1b, M0: The tumor is any size and might have grown slightly outside the thyroid gland (T1 to T3). It has spread to certain lymph nodes in the neck (cervical nodes) or to lymph nodes in the upper chest (superior mediastinal nodes) or behind the throat (retropharyngeal nodes) (N1b), but it has not spread to distant sites (M0).

Stage IVB (T4b, any N, M0): The tumor is any size and has grown either back toward the spine or into nearby large blood vessels (T4b). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVC (any T, any N, M1): The tumor is any size and might or might not have grown outside the thyroid (any T). It might or might not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

Medullary thyroid cancer

Age is not a factor in the stage of medullary thyroid cancer.

Stage I (T1, N0, M0): The tumor is 2 cm or less across and has not grown outside the thyroid (T1). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage II: One of the following applies:

T2, N0, M0: The tumor is more than 2 cm but is not larger than 4 cm across and has not grown outside the thyroid (T2). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

T3, N0, M0: The tumor is larger than 4 cm or has grown slightly outside the thyroid (T3), but it has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage III (T1 to T3, N1a, M0): The tumor is any size and might have grown slightly outside the thyroid (T1 to T3). It has spread to lymph nodes around the thyroid in the neck (N1a) but not to other lymph nodes or to distant sites (M0).

Stage IVA: One of the following applies:

T4a, any N, M0: The tumor is any size and has grown beyond the thyroid gland and into nearby tissues of the neck (T4a). It might or might not have spread to nearby lymph nodes (any N). It has not spread to distant sites (M0).

T1 to T3, N1b, M0: The tumor is any size and might have grown slightly outside the thyroid gland (T1 to T3). It has spread to certain lymph nodes in the neck (cervical nodes) or to lymph nodes in the upper chest (superior mediastinal nodes) or behind the throat (retropharyngeal nodes) (N1b), but it has not spread to distant sites (M0).

Stage IVB (T4b, any N, M0): The tumor is any size and has grown either back toward the spine or into nearby large blood vessels (T4b). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVC (any T, any N, M1): The tumor is any size and might or might not have grown outside the thyroid (any T). It might or might not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

Anaplastic (undifferentiated) thyroid cancer

All anaplastic thyroid cancers are considered stage IV, reflecting the poor prognosis of this type of cancer.

Stage IVA (T4a, any N, M0): The tumor is still within the thyroid (T4a). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVB (T4b, any N, M0): The tumor has grown outside the thyroid (T4b). It might or might not have spread to nearby lymph nodes (any N), but it has not spread to distant sites (M0).

Stage IVC (any T, any N, M1): The tumor might or might not have grown outside of the thyroid (any T). It might or might not have spread to nearby lymph nodes (any N). It has spread to distant sites (M1).

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