What is Thyroid Cancer?
The thyroid gland is located in the neck. It is responsible for producing hormones that affect food processing, energy and other bodily functions. There are four types of thyroid cancer:
- Papillary is the most common type, making up 70-80% of all thyroid cancers. It usually grows slowly and can spread to the lymph nodes, but is often treatable.
- Follicular makes up 10-15% of thyroid cancers. The average age at diagnosis is older than papillary cancer. It also grows slowly and can spread to lymph nodes in the neck. Follicular cancer is more likely than papillary to grow into blood vessels and spread to distant areas, particularly the lungs and bones.
- Medullary accounts for about 5-10% of thyroid cancers. It is more likely to run in families and may be associated with other endocrine problems. Medullary thyroid cancer is the only thyroid cancer that can be diagnosed by genetic testing. A positive test for the RET proto-oncogene can lead to an early diagnosis.
- Anaplastic is the most advanced and aggressive thyroid cancer. It is least likely to respond to treatment, but also the rarest, accounting for less than 5% of all thyroid cancers.
Risk Factors, Signs & Symptoms
Risk Factors for Thyroid Cancer
The following are common risk factors for the disease:
- Age/Sex - Thyroid cancer mostly affects people over the age of 45. People diagnosed with anaplastic thyroid cancer are usually over 60. Women are more likely to get thyroid cancer than men.
- Family History - A family history of thyroid cancer increases your risk. Medullary thyroid cancer can be passed from parent to child through a change in a gene called RET. Nearly everyone with the changed RET gene develops medullary thyroid cancer.
- Iodine - Iodine is a substance found in shellfish and iodized salt. Too little iodine in the diet may increase the risk of follicular thyroid cancer. Too much may increase the risk of papillary thyroid cancer.
- Personal History - People with a history of goiters or benign thyroid nodules have an increased risk of 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.
Signs & Symptoms
Early thyroid cancer often does not have symptoms. As the cancer grows, symptoms may include:
- Hoarseness or voice changes
- Lump in the front of the neck
- Pain in the throat or neck that does not go away
- Swollen lymph nodes in the neck
- Trouble swallowing or breathing
Diagnosis and Staging
Nodules on the thyroid are often discovered through routine physical exams. If a thyroid nodule is detected, your doctor will ask about your personal and family medical history and feel your neck for lumps or swelling. Once you learn the results of the tests or procedures, you will be able to work with your health care team to make thoughtful decisions.
You also will likely have one or more of the following tests:
Blood Tests - These check for abnormal levels of TSH (thyroid-stimulating hormone) in the blood. Levels that are too high or too low indicate the thyroid isn’t functioning properly.
Ultrasound - Sound waves and a computer are used to create a picture of thyroid nodules that are too small to be felt. This test shows the size and shape of the nodule and whether it is solid or filled with fluid. Solid nodules can be cancerous.
Thyroid Scan - This test involves swallowing a small amount of a radioactive substance and undergoing a scan. The thyroid nodules are labeled “hot” or “cold” depending on how they absorb the substance. Cold nodules can be cancer.
Biopsy - A pathologist looks at a sample of tissue from the nodule under a microscope to check for cancer cells. This test is the only sure way to diagnose thyroid cancer. It can be done in two ways, either through fine needle aspiration or a surgical biopsy.
- Fine Needle Aspiration: Involves a thin needle; commonly used to diagnose thyroid cancer
- Surgical Biopsy: An operation to remove a nodule from the thyroid; used if the results of the fine needle aspiration are uncertain or if a doctor suspects follicular thyroid cancer
Treatment and Side Effects
Treatment options for thyroid cancer depend on the type, the size of the nodule, the person’s age and whether the cancer has spread.
- Thyroid hormone treatment
- Radioactive iodine therapy
- External radiation therapy
Most people with thyroid cancer have surgery to remove either part (lobectomy) or all (thyroidectomy) of the thyroid. A lobectomy is more common with follicular or papillary cancer. People who have a lobectomy sometimes have a second surgery to remove the rest of the thyroid. A thyroidectomy can be used for all types of thyroid cancer.
Hormone pills help restore the thyroid function or slow the growth of cancer. They are used after surgery or as part of the treatment plan for papillary or follicular cancer.
Radioactive iodine, given as a liquid or pill, kills thyroid cancer cells and normal thyroid cells that remain in the body after surgery. This therapy is used for papillary or follicular cancer; medullary and anaplastic cancers rarely respond to this treatment. Most radiation goes away within a week.
External radiation is used to treat thyroid cancer that cannot be treated with surgery or radioactive iodine or cancer that has returned. A large machine directs high-energy radiation rays at the neck to kill cancer cells. Radiation can also help with bone pain from cancer that has spread.
Drugs, given by injection to a vein, can kill cancer cells. Chemotherapy is used to treat anaplastic thyroid cancer and sometimes to reduce symptoms of medullary cancer.
After treatment, it is important to have regular exams to check thyroid hormone levels. Blood tests and imaging tests may be used to monitor recovery and make sure cancer has not returned. If thyroid cancer comes back, it is often found in the neck, lungs or bones.
Overall the prognosis for thyroid cancer is very good. People with papillary carcinoma who have a primary tumor that is confined to the thyroid gland have an excellent outlook. The prognosis is not quite as good in people over the age of 40 and in people with tumors larger than 4 centimeters in diameter. Even when cure is not possible, people often live a long time and feel well despite their thyroid cancer.