What is Thyroid Cancer?
- The thyroid gland is located low in the front of the neck, below the Adam's apple. The gland is shaped like a butterfly and wraps around the windpipe or trachea. The two wings or lobes on either side of the windpipe are joined together by a bridge, called the isthmus, which crosses over the front of the windpipe.
- Thyroid cancer occurs in all age groups, although its incidence increases with age, especially after 30 years of age. The more aggressive forms of thyroid cancer are more commonly found in older patients.
- Thyroid cancer occurs three times more frequently in women than in men.
- Thyroid cancer originates from one of two different types of thyroid cells: follicular cells or so-called parafollicular, or C cells.
Thyroid Cancer Causes
There are four major types of thyroid cancers, listed below in order of decreasing frequency:
Papillary (includes follicular variant papillary thyroid carcinoma)
Papillary thyroid cancer (PTC) is the most common type of thyroid cancer and accounts for more than two-thirds of all thyroid cancers. There is a higher risk of developing this tumor in persons who have had previous head and neck radiation.
Most patients will not die from papillary thyroid cancer. They are considered low risk if:
- They are younger than 45 years of age.
- They have small tumors.
- There is no invasion of surrounding structures and no metastasis (distant spread).
The spread of papillary thyroid cancer to lymph nodes may indicate recurrence, but it is not associated with a higher chance of death. If distant metastases occur, the pattern of spread includes the lung, bone, and other soft tissue - usually in older people.
Follicular variant papillary thyroid cancer is a type of papillary thyroid cancer that has a survival rate similar to that of papillary thyroid cancer. Overall, papillary thyroid cancer is associated with a high survival rate.
Follicular (includes Hurthle cell and insular carcinoma)
Follicular thyroid cancer (FTC) occurs more in older patients compared to papillary thyroid cancer. The diagnosis of "malignancy" depends on the spread to local tissue and blood vessels. Like papillary thyroid cancer, the patient's age, size of tumor, and the extent that the tumor has spread can predict severity of disease.
Like papillary cancer, follicular cancer develops from the follicular cells and tends to grow slowly.
Variants of follicular thyroid cancer include insular carcinoma and Hurthle cell carcinoma of the thyroid. These tumors are less likely to concentrate radioactive iodine.
Medullary carcinoma of the thyroid originates from the thyroid parafollicular, or C cells. C cells produce a hormone called calcitonin, which can be measured and used as a marker of medullary carcinoma. Medullary carcinoma can occur "sporadically" with no association, with other endocrine diseases, or may have a genetic basis when associated with familial medullary carcinoma or the multiple endocrine neoplasia syndromes (MEN). Multiple endocrine neoplasia syndromes are a group of endocrine diseases that result from an inherited gene mutation. With multiple endocrine neoplasia syndromes which include medullary carcinoma of the thyroid, the adrenal glands, the parathyroid glands, and the surface of the mouth may be affected in addition to the thyroid.
The manner of presentation is different when comparing the sporadic form usually presents with a solitary thyroid mass, whereas the hereditary form usually presents with bilateral thyroid masses in a multifocal fashion.
Medullary carcinoma can include multiple tumors in both lobes of the thyroid and frequently spreads to local lymph nodes, both in the neck and the mediastinum.
Anaplastic thyroid cancer
Anaplastic thyroid cancer is a rare and fast-growing type of thyroid cancer.
Some genetic mutations are related to some thyroid cancers. Damage to DNA can cause these gene mutations due to changes that occur during the natural aging process, radiation exposure, or radiation treatments (as used in the past for skin conditions and head and neck conditions).
Anaplastic thyroid cancer typically occurs in older patients and accounts for less than 5% of all thyroid cancers. One-fifth of these patients may have a current history of another cancer, including a more common form of thyroid cancer. Anaplastic cancer is the most aggressive thyroid cancer. Local invasion and distant spread occur rapidly to other sites, including lymph nodes and the lungs.
Thyroid Cancer Symptoms
A thyroid nodule larger than 1 cm that is found to have decreased iodine uptake on a nuclear medicine thyroid scan needs to be evaluated with a fine needle aspiration biopsy.
Thyroid Cancer Exams and Tests
The diagnosis of thyroid cancer is usually established by examination of cells obtained from a fine-needle aspiration biopsy or a surgical biopsy of a thyroid nodule.
In a fine-needle aspiration biopsy, a thin needle is inserted through the skin into the thyroid nodule and cells are withdrawn into a syringe and sent to the laboratory for analysis by a pathologist.
Blood tests are generally not useful in determining whether a particular thyroid nodule is cancerous. Most patients with thyroid cancer have normal blood levels of thyroid hormones, including a thyrotropin (TSH) level.
Other imaging studies may be useful. An ultrasound of the neck can help identify local cancer spreading to the lymph nodes and blood vessels. Nuclear medicine imaging of the thyroid with radioactive iodine (I-123 or I-131) can identify a thyroid nodule with decreased iodine uptake (sometimes referred to as a "cold" nodule) that may warrant further testing for cancer with a fine-needle aspiration biopsy. Computerized tomography (CT) of the neck can be used to outline the extent of the thyroid tumor into the lymph nodes, blood vessels, and upper GI tract. Computerized tomography is never performed with IV contrast material if the patient is going to have a radioactive iodine scan or treatment within six to eight weeks.
Thyroid Cancer Treatment
Surgery to remove all cancer in the neck and any cancerous lymph nodes is the initial therapy for most thyroid cancers. Complications are rare when the procedure is performed by an experienced thyroid surgeon.
Radioactive Iodine using I-131 is typically used as a follow-up to surgery, or "adjuvant" treatment in papillary and follicular thyroid cancers. This treatment is usually given two to six weeks following thyroid surgery. It involves giving high doses of I-131 in a liquid or pill form. Patients undergoing this treatment must restrict their dietary intake of iodine for approximately five to14 days before the treatment and must restrict their contact with children and pregnant women for three to seven days after treatment. The goals of this treatment include destruction of any remaining thyroid tissue in the neck, a reduction in cancer recurrence rate, and improved survival.
Radiation treatment, known as external-beam radiation therapy, is used in patients with cancer that cannot be treated with surgery or is unresponsive to radioactive iodine, as well as for older patients with cancer that has distant spread. Radiation is sometimes combined with chemotherapy.
Classical chemotherapy is rarely useful, but sometimes tried for progressive diseases unresponsive to radioactive iodine or radiation.
There are two new FDA approved targeted agents for the treatment of metastatic medullary thyroid carcinoma. These drugs are vandetenib (Capresa) and cabozantinib (Cometriq). In addition, the drug Lenvima (levatinib) has recently received FDA approval for the treatment of refractory differentiated thyroid cancers of papillary and follicular type. Levima appears possibly more effective than sorafenib (Nexavar), also approved for these patients with differentiated (papillary and follicular) thyroid cancer patients who are no longer responsive to radioactive iodine.
Treatments for the four thyroid cancer types
Papillary thyroid cancer responds to treatment with surgery and radioactive iodine.
Follicular thyroid cancer responds to treatment with surgery and radioactive iodine treatment.
Medullary thyroid cancer must be treated with surgical removal of the entire thyroid gland in addition to complete removal of all neck lymph nodes and fatty tissue. This type of cancer does not respond to radioactive iodine therapy and has a much lower cure rate than either papillary or follicular thyroid cancer. After surgery, patients should be followed every six to 12 months with blood calcitonin and CEA levels to watch for recurrence.
Anaplastic thyroid cancer often cannot be cured with surgery by the time of diagnosis (due to spread of the disease). This cancer is not responsive to radioactive iodine and may require radiation and chemotherapy, or even tracheotomy if the disease is locally advanced and is causing impingement on an airway.
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Thyroid Cancer Follow-up
Once any remaining thyroid tissue is removed or destroyed, thyroid hormone replacement must be taken to prevent hypothyroidism and suppress the stimulation of thyroid tissue. The goal of treatment with thyroid hormone replacement therapy is to achieve borderline higher, or slightly higher than normal, levels of thyroid hormone.
Iodine123 and Iodine131 whole-body scans can be used to monitor the effects of treatment in papillary and follicular thyroid cancer patients. A post-therapy scan approximately one week after radioactive iodine treatment can reveal small areas of metastasis or residual disease. After initial therapy, follow-up scans can be performed approximately 12 months after surgery or earlier for obvious recurrent disease. Scans should be done only after the patient is made hypothyroid, either by discontinuing thyroid hormone replacement or through using an injectable form of thyrotropin (rTSH).
Thyroglobulin blood levels can be useful for follow-up in some patients and are measured at three- to 12-month intervals following treatment. Thyroglobulin is a protein made in thyroid follicular cells. In patients with thyroid cancer who have had their thyroid removed, blood levels of thyroglobulin can be used as a marker of thyroid cancer recurrence.
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