Thyroid Cancer
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. It has two parts, or lobes. The two lobes are separated by a thin
section called the isthmus.
A
healthy thyroid is a little larger than a 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 iodized salt.
The
thyroid cancer is the cancer that forms in the thyroid gland.
The three main types of thyroid cancer are papillary, follicular, medullary
thyroid cancer. The three types are based on how the cancer cells look under a
microscope.
- Papillary and follicular thyroid cancers begin in the follicular cells
of the thyroid. Most papillary and follicular thyroid cancers tend to grow
slowly. If they are detected early, most can be treated successfully.
- Medullary thyroid cancer begins in C cells, not follicular cells.
Medullary thyroid cancer is easier to control if it is found and treated before
it spreads to other parts of the body.
Risk Factors
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.
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. (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.)
Another source of radiation is
radioactive fallout. This includes fallout from atomic weapons testing, nuclear
power plant accidents and releases from atomic weapons production plants. 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.
Females. 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.
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.
Symptoms
Early thyroid cancer often does not cause symptoms. But as the cancer
grows, symptoms may include:
- A lump in the front of the neck near the Adam's apple;
- difficulty speaking in a normal voice;
- Swollen lymph nodes, especially in the neck;
- Difficulty swallowing or breathing;
- Pain in the throat.
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