Most thyroid cancers are asymptomatic (without symptoms). A nodule (lump or bump) in the thyroid that can be felt is the most common indication of thyroid cancer. The thyroid is a gland located in the neck. Occasionally, thyroid cancer can cause pain, hoarseness, and difficulty swallowing or the patient may experience swollen lymph nodes.
There is a known association between radiation exposure, especially as a child, and a family history of thyroid cancer. Certain types can occur in patients with a family history of the disease. However, for the majority of patients, the cause is unknown.
Differentiated thyroid cancers disproportionately affect women and young adults. Women are five times more likely than men to be diagnosed with thyroid cancer. Medullary thyroid cancer does not show a gender predilection.
Thyroid nodules can be found with ultrasound but a biopsy is required to diagnose cancer, usually by fine needle aspiration, guided by ultrasound. Thyroid scans using a radioactive isotope of iodine (I-131) can be useful in detecting suspicious nodules or distant metastases in differentiated thyroid cancer. The thyroid tissue naturally absorbs iodine to make hormones. Ingesting a small amount of radioactive iodine, then undergoing a scan, can determine how much iodine is absorbed. Nodules that absorb more iodine than surrounding tissue are termed hot, while nodules that absorb less iodine are termed cold. Hot nodules are unlikely to be cancerous, while cold nodules may be malignant or benign.
Thyroid cancer is first treated with surgery, followed with radioactive iodine. After surgery, patients are required to start life-long thyroid hormone replacement therapy. Systemic (body-wide) chemotherapy is rarely used to treat thyroid cancer.
The type of surgery required depends upon the type of thyroid cancer, the size or number of tumors and the involvement of lymph nodes. Most often a total thyroidectomy is done to remove the thyroid. Lymph nodes are often removed to check for regional spread. Low-risk patients sometimes have less extensive surgery.
Recovery from surgery usually takes a few weeks. Patients are typically in the hospital for a few days to a week after surgery. Surgery does carry risks of damage to the laryngeal nerve, which may cause hoarseness, or to the parathyroid glands, which regulate calcium levels in the blood. However, when surgery is performed by an experienced surgeon, these risks are minimal.
The thyroid naturally takes up iodine to make hormones. I-131 is an unstable form of the element iodine (an isotope) that tries to stabilize itself by emitting small amounts of energy in the form of radiation. After a thyroidectomy, radioactive iodine (I-131) is usually used to destroy any remaining thyroid tissue. Radioactive iodine (RAI) is given orally approximately two weeks after surgery. A patient is kept in isolation for a few days after it is administered to prevent him or her from exposing others to the radiation. RAI is useful in differentiated thyroid cancers and plays a role in destroying distant metastases. RAI treatment may temporarily cause decreased saliva production and changes in taste. The lowest effective dose of radiation is always given to minimize side effects.
RAI is used in much lower doses in post-treatment thyroid scans to check for disease activity and spread. Before RAI is administered, patients are asked to go off their replacement thyroid hormones for about two weeks to elevate the amount of thyroid stimulating hormone (TSH). TSH promotes the uptake of RAI. When patients are off their thyroid hormones, they may experience symptoms of hypothyroidism, such as fatigue, weight gain or mood change. A synthetic TSH is available, allowing patients to still take thyroid hormones and not experience hypothyroidism. The dose of RAI is much lower for post-treatment scans than for RAI ablation.
Hormone replacement is necessary after a thyroidectomy. Synthetic hormones are readily available and must be taken for the remainder of a patient’s life. Synthetic thyroid hormones are given at a slightly increased level than normal to suppress TSH. TSH stimulates growth of the thyroid so suppression of TSH is necessary to prevent disease recurrence or spread. Patients will be monitored by an endocrinologist to manage hormone levels.
Chemotherapy is rarely used to treat thyroid cancer. Because of the high rates of cure using surgery and RAI alone, it is often not necessary. However, it may be used if the disease is recurrent or very aggressive and other methods have been exhausted. Chemotherapy is more commonly used in older patients.
The prognosis for young adults diagnosed with thyroid cancer is excellent. The overall survival rate in patients with local or loco-regional disease is 97 percent to 100 percent. Those patients who are 15 to 29 years of age have greater than a 99 percent chance of surviving five years.
However, thyroid cancer recurs in about 15 percent to 35 percent of cases, and can recur decades after initial treatment. It most often returns in the lymph nodes in the neck. Regular follow-up by your doctor with a physical exam is the best way to check for recurrence. Rarely, thyroid cancer can metastasize to the lungs or bones.
Thyroid cancer is the second most common cancer diagnosed during pregnancy, after breast cancer. Surgery usually can be postponed until the mother has given birth. If surgery is necessary sooner, it may be performed in the second trimester. RAI is not given during pregnancy or while breastfeeding. Women have an increased need for thyroid hormones during pregnancy. Synthetic thyroid hormones may be given to suppress TSH levels and to stop disease progression.