Cancer that forms in the thyroid
gland (an organ at the base of the throat that makes hormones that help
control heart rate, blood
pressure, body temperature, and weight). The four main types of thyroid
cancer are papillary, follicular, medullary, and anaplastic thyroid cancer.
These four types are based on how the cancer cells look under a microscope.
The thyroid gland
The thyroid is a gland
in the neck. It has two kinds of cells that make hormones.
Follicular cells make thyroid hormone,
which affects heart rate, body temperature, and energy level. C cells make
calcitonin, a hormone that helps control
the level of calcium in the blood.
The thyroid is shaped like a butterfly and lies at the front of the neck,
beneath the larynx (voice box). It has two
parts, or lobes. The two lobes are separated by a thin section called the
A healthy thyroid is a little larger than a U.S. quarter. It usually cannot
be felt through the skin. A swollen lobe might look or feel like a lump
in the front of the neck. A swollen thyroid is called a goiter.
Most goiters are caused by not enough iodine
in the diet. Iodine is a substance found in shellfish and iodized salt.
Who is at risk from thyroid cancer?
No one knows the exact causes of thyroid cancer. Doctors can seldom explain
why one person gets this disease and another does not. However, it is clear
that thyroid cancer is not contagious. No one can "catch" cancer from another
Research has shown that people with certain risk factors are more likely
than others to develop thyroid cancer. A risk factor is anything that increases
a person's chance of developing a disease.
The following risk factors are associated with an increased chance of developing
Most people who have known risk factors do not get thyroid cancer. On the
other hand, many who do get the disease have none of these risk factors.
People who think they may be at risk for thyroid cancer should discuss this
concern with their doctor. The doctor may suggest ways to reduce the risk
and can plan an appropriate schedule for checkups.
- Radiation. People exposed to high levels of radiation
are much more likely than others to develop papillary or follicular
One important source of radiation exposure is treatment with X-rays.
Between the 1920s and the 1950s, doctors used high-dose X-rays to treat
children who had enlarged tonsils, acne,
and other problems affecting the head and neck. Later, scientists found
that some people who had received this kind of treatment developed thyroid
cancer. (Routine diagnostic X-rays – such as dental X-rays or
chest X-rays – use very small
doses of radiation. Their benefits nearly always outweigh their risks.
However, repeated exposure could be harmful, so it is a good idea for
people to talk with their dentist and doctor about the need for each
X-ray and to ask about the use of shields to protect other parts of
Another source of radiation is radioactive fallout. This includes fallout
from atomic weapons testing (such as the testing in the United States
and elsewhere in the world, mainly in the 1950s and 1960s), nuclear
power plant accidents (such as the Chernobyl accident in 1986), and
releases from atomic weapons production plants (such as the Hanford
facility in Washington state in the late 1940s). Such radioactive fallout
contains radioactive iodine (I-131). People who were exposed to one
or more sources of I-131, especially if they were children at the time
of their exposure, may have an increased risk for thyroid diseases.
- Family history. Medullary thyroid cancer can be caused
by a change, or alteration, in a gene called
RET. The altered RET gene can be passed from parent to child. Nearly
everyone with the altered RET gene will develop medullary thyroid cancer.
A blood test can detect an altered RET gene. If the abnormal gene is
found in a person with medullary thyroid cancer, the doctor may suggest
that family members be tested. For those found to carry the altered
RET gene, the doctor may recommend frequent lab tests or surgery to
remove the thyroid before cancer develops. When medullary thyroid cancer
runs in a family, the doctor may call this "familial medullary thyroid
cancer" or "multiple endocrine neoplasia (MEN) syndrome." People with
the MEN syndrome tend to develop certain other types of cancer.
A small number of people with a family history of goiter or certain
precancerous polyps in the colon
are at risk for developing papillary thyroid cancer.
- Being female. In the United States, women are two
to three times more likely than men to develop thyroid cancer.
- Age. Most patients with thyroid cancer are more than
40 years old. People with anaplastic thyroid cancer are usually more
than 65 years old.
- Race. In the United States, white people are more
likely than African Americans to be diagnosed with thyroid cancer.
- Not enough iodine in the diet. The thyroid needs
iodine to make thyroid hormone. In the United States, iodine is added
to salt to protect people from thyroid problems. Thyroid cancer seems
to be less common in the United States than in countries where iodine
is not part of the diet.
What are the symptoms of thyroid cancer?
Early thyroid cancer often does not cause symptoms. But as the cancer grows,
symptoms may include:
These symptoms are not sure signs of thyroid cancer. An infection, a benign
goiter, or another problem also could cause these symptoms. Anyone with
these symptoms should see a doctor as soon as possible. Only a doctor can
diagnose and treat the problem.
- A lump, or nodule, in the front of the neck near the Adam's apple;
- Hoarseness or difficulty speaking in a normal voice;
- Swollen lymph nodes, especially
in the neck;
- Difficulty swallowing or breathing; or
- Pain in the throat or neck.
How is thyroid cancer diagnosed?
If a person has symptoms that suggest thyroid cancer, the doctor may perform
a physical exam and ask about the patient's personal and family medical
history. The doctor also may order laboratory tests and imaging tests to
produce pictures of the thyroid and other areas.
The exams and tests may include the following:
- Physical exam. The doctor will feel the neck, thyroid,
voice box, and lymph nodes in the neck for unusual growths (nodules)
- Blood tests.
The doctor may test for abnormal levels (too low or too high) of thyroid-stimulating
hormone (TSH) in the blood. TSH is made by the pituitary
gland in the brain. It stimulates the release of thyroid hormone.
TSH also controls how fast thyroid follicular cells grow.
If medullary thyroid cancer is suspected, the doctor may check for abnormally
high levels of calcium in the blood. The doctor also may order blood
tests to detect an altered RET gene or to look for a high level of calcitonin.
The ultrasound device uses sound waves that people cannot hear. The
waves bounce off the thyroid, and a computer uses the echoes to create
a picture called a sonogram. From the picture, the doctor can see how
many nodules are present, how big they are, and whether they are solid
or filled with fluid.
- Radionuclide scanning. The doctor may order a nuclear
medicine scan that uses a very small amount of radioactive material
to make thyroid nodules show up on a picture. Nodules that absorb less
radioactive material than the surrounding thyroid tissue are called
cold nodules. Cold nodules may be benign or malignant. Hot nodules take
up more radioactive material than surrounding thyroid tissue and are
- Biopsy. The removal
of tissue to look for cancer cells is called a biopsy. A biopsy can
show cancer, tissue changes that may lead to cancer, and other conditions.
A biopsy is the only sure way to know whether a nodule is cancerous.
The doctor may remove tissue through a needle or during surgery:
- Fine-needle aspiration. For most patients, the doctor removes
a sample of tissue from a thyroid nodule with a thin needle. A pathologist
looks at the cells under a microscope to check for cancer. Sometimes,
the doctor uses an ultrasound device to guide the needle through
- Surgical biopsy. If a diagnosis cannot be made from the
fine-needle aspiration, the doctor may operate to remove the nodule.
A pathologist then checks the tissue for cancer cells.
A person who needs a biopsy may want to ask the doctor the following
- What kind of biopsy will I have?
- How long will the procedure take? Will I be awake? Will it hurt?
- Will I have a scar on my neck after the biopsy?
- How soon will you have the results? Who will explain them to me?
- If I do have cancer, who will talk to me about treatment? When?
Staging the disease
If the diagnosis is thyroid cancer, the doctor needs to know the stage,
or extent, of the disease to plan the best treatment. Staging is a careful
attempt to learn whether the cancer has spread and, if so, to what parts
of the body.
The doctor may use ultrasonography, magnetic
resonance imaging (MRI), or computed tomography (CT) to find out whether
the cancer has spread to the lymph nodes or other areas within the neck.
The doctor may use a nuclear medicine scan of the entire body, such as a
radionuclide scan known as the "diagnostic I-131 whole body scan," or other
imaging tests to learn whether thyroid cancer has spread to distant sites.
How is thyroid cancer treated?
Read about how thyroid cancer
Source: National Cancer Institute