Thyroid Cancer (cont.)
What causes thyroid cancer, and what are risk
factors of 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 person.
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 thyroid cancer:
- Radiation. People exposed to high levels of radiation are much more likely
than others to develop papillary or follicular thyroid cancer.
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 the
body.)
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 Chornobyl [also called 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.
People who are concerned about their exposure to radiation from medical
treatments or radioactive fallout may wish to ask the Cancer Information Service
at 1-800-4-CANCER about additional sources of information.
- 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.
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.
Next: What are symptoms of thyroid cancer? »
Cancer RSS