Overview of Thyroid Cancer
Medically reviewed by Dr. C.H. Weaver M.D. Medical Editor 10/2018
Thyroid cancer affects women more often than men and has been increasing over the last decade. Thyroid cancer is commonly first detected as a palpable thyroid gland during a physical exam. Overall there is estimated to be 56,000 individuals diagnosed with thyroid cancer in the United States each year with only 2,000 dying from their disease.,
The Thyroid Gland
Located just below the Adam’s apple and wrapped around the windpipe, the butterfly-shaped thyroid gland produces hormones that regulate the body’s metabolism, which controls virtually every cell, tissue, and organ in the body. The thyroid absorbs iodine from consumed food and uses it (through its follicle cells) to manufacture the thyroid protein thyroglobulin and two main hormones, thyroxine (T-4) and triiodothyronine (T-3), which control body temperature, heart rate, blood pressure, and weight.1 The thyroid gland (through its parafollicular, or C, cells) also produces calcitonin, a hormone that helps regulate calcium in the blood. Four or more tiny parathyroid glands on its surface make parathyroid hormone, which helps the body maintain a healthy calcium level.
The main initial diagnostic test of the thyroid is evaluation with an iodine (I 131) scan. If this test shows that the I 131 is not taken up in an area of the gland, the nodule is said to be “cold” and cancer is suspected. The overall incidence of cancer in a cold nodule is ~15% and is higher in people younger than 40 years of age and those with calcifications.,
Types of Thyroid Cancer
Cancer may arise from different cells of the thyroid gland. By evaluating a sample of the cancer under a microscope, doctors can determine the type of thyroid cancer. There are four main types of thyroid cancer. The thyroid gland may occasionally be the site of other primary tumors, including sarcomas, lymphomas, epidermoid carcinomas, and teratomas. The thyroid may also be the site of metastasis from other cancers, particularly of the lung, breast, and kidney.
Papillary: Papillary tumors are the most common form of thyroid cancer, accounting for more than 70% of all cases. Papillary cancers are typically irregular or solid masses that arise from otherwise normal thyroid tissue. More than half of papillary cancers have spread to lymph nodes in the neck. However, papillary cancers rarely spread to distant locations in the body. Papillary cancers typically occur in younger patients (30-50 years) and are commonly associated with a prior exposure to radiation. Patients with papillary cancer are highly curable with currently available treatment techniques.
Follicular: Follicular cancers account for a smaller percentage of all thyroid cancers (approximately 15%) and rarely occur after radiation exposure. Follicular cancers are more aggressive; they tend to invade blood vessels rather than lymph nodes, and distant spread is therefore more common. Potential sites of distant spread include the lung, bone, brain, liver, bladder, and skin. Patients over 40 have more aggressive disease that is more difficult to treat. Nonetheless, most follicular cancers are very curable.
Medullary: There are two subtypes of medullary thyroid cancer: sporadic and familial. Sporadic almost always occurs on both sides of the thyroid gland. Familial tumors may be malignant or benign and may be associated with a variety of symptoms.
Approximately half of medullary thyroid cancers have spread to lymph nodes. Prognosis depends on the extent of disease at diagnosis—especially spread to lymph nodes—and the ability to completely remove the cancer with surgery.
Anaplastic: Anaplastic thyroid cancer is a rare disease that may also be called undifferentiated cancer. This type of thyroid cancer is very aggressive, grows rapidly, and commonly extends beyond the thyroid gland. It typically occurs in older patients and is characterized by extensive spread in the neck area and rapid progression. Patients typically die of their disease within months of diagnosis.
Well-differentiated tumors are highly treatable and usually curable. Poorly differentiated tumors are less common, aggressive, metastasize early, and have a poorer prognosis.
Symptoms & Signs of Thyroid Cancer
Thyroid caner is typically detected when an individual or their physician identifies a lump or nodule in the thyroid gland, often during routine physical examination. Additional symptoms or sign attributable to thyroid cancer are uncommon.
Cause of Thyroid Cancer
Thyroid cancer begins when healthy cells acquire a genetic change (mutation) that causes them to turn into abnormal cells. Most thyroid cancers develop sporadically, which means for no known reason. Development of thyroid cancer however can occur as a result of radiation exposure and occurs in some hereditary syndromes.,
Risk Factors for Thyroid Cancer
A risk factor is anything that increases a person’s chance of developing cancer. Risk factors can influence the development of cancer but most do not directly cause cancer. Many individuals with risk factors will never develop cancer and others with no known risk factors will.
Patients with a history of radiation therapy to the head and neck have an increased risk of cancer and other abnormalities of the thyroid gland. Cancer of the thyroid gland may appear as early as 5 years after radiation therapy and may appear 20 or more years later.,, Radiation exposure as a consequence of nuclear fallout has also been associated with a high risk of thyroid cancer, especially in children.,
Risk factors for thyroid cancer include the following:,
- Radiation exposure.
- Family history of thyroid disease.
- Multiple endocrine neoplasia (MEN) syndrome.
- RET gene mutation.
- A history of thyroid goiter.
- Female gender.
- Asian race.
Diagnosis & Tests for Thyroid Cancer
Although thyroid cancer is essentially symptomless, if you see or feel any lumps in the neck area or experience prolonged hoarseness, don’t put off seeking an appointment with an endocrinologist or thyroidologist. Once you’ve seen the specialist, the process of diagnosis might involve a number of tests, including a thyroid ultrasound, blood tests, fine needle aspiration biopsy, nodule biopsy, a radioactive iodine uptake (RAI-U) nuclear scan, and magnetic resonance imaging (MRI).
An RAI-U nuclear scan is usually performed before any biopsy and involves taking a small amount of radioactive iodine to scan the body for “cold” spots. Nodules that absorb less substance than the thyroid tissue around them are called cold nodules and may be cancerous.) Although routine thyroid blood tests (checking for abnormal levels of thyroid-stimulating hormone [TSH] in the blood) do not result in an abnormal reading for all thyroid cancer—such as papillary—in some cases blood work can indicate the possibility of another type of thyroid cancer: medullary. If the doctor suspects medullary cancer, additional blood work will check for high levels of calcitonin, which is unique to all the thyroid cancers that can occur.
A biopsy is the only certain way to confirm a diagnosis of cancer. When performing a biopsy, the doctor takes a sample of tissue for testing in a laboratory. The sample may be removed using a fine needle and or may be removed during the surgery to treat the nodule. If initial tests indicate that the nodule is cancerous, a surgery will be scheduled to remove as much of the cancer as possible and to determine the extent of spread or the stage of the cancer.
Fine needle aspiration: Fine needle aspiration is a technique that uses a needle and syringe to withdraw a sample of the cells from a thyroid nodule. The cells can then be evaluated under a microscope to determine if they are cancerous or benign. Since many thyroid nodules are benign, this technique provides a minimally invasive way to determine if surgery is necessary.
Staging of Thyroid Cancer
When diagnosed with cancer further tests are necessary to determine the extent of spread (stage) of the cancer. Cancer’s stage is a key factor in determining the best treatment. The stage of cancer may be determined at the time of diagnosis or it may be necessary to perform additional tests. In addition to a through history and physical exam, tests used to diagnose and stage thyroid cancer may include the following:
- Ultrasound: Ultrasound uses high frequency sound waves and their echoes to create a two-dimensional image that is projected on a screen. Ultrasound is a simple procedure that may allow doctors to determine if a thyroid nodule is cancerous or benign based on the appearance of the image that is produced. A limitation of ultrasound is that it does not produce a sample of the cells that can be evaluated under a microscope.
- Positron emission tomography (PET): Positron emission tomography scanning is an advanced technique for imaging body tissues and organs. One characteristic of living tissue is the metabolism of sugar. Prior to a PET scan, a substance containing a type of sugar attached to a radioactive isotope (a molecule that emits radiation) is injected into the patient’s vein. The cancer cells “take up” the sugar and attached isotope, which emits positively charged, low energy radiation (positrons) that create the production of gamma rays that can be detected by the PET machine to produce a picture. If no gamma rays are detected in the scanned area, it is unlikely that the mass in question contains living cancer cells.
- Computed Tomography (CT) Scan: A CT scan is a technique for imaging body tissues and organs, during which X-ray transmissions are converted to detailed images, using a computer to synthesize X-ray data. A CT scan is conducted with a large machine positioned outside the body that can rotate to capture detailed images of the organs and tissues inside the body.
Precision Cancer Medicine
The purpose of precision cancer medicine is not to categorize or classify cancers solely by site of origin, but to define the genomic alterations in the cancers DNA that are driving that specific cancer. Precision cancer medicine utilizes molecular diagnostic & genomic testing, including DNA sequencing, to identify cancer-driving abnormalities in a cancer’s genome. Once a genetic abnormality is identified, a specific targeted therapy can be designed to attack a specific mutation or other cancer-related change in the DNA programming of the cancer cells. Precision cancer medicine uses targeted drugs and immunotherapies engineered to directly attack the cancer cells with specific abnormalities, leaving normal cells largely unharmed. Precision medicines are being developed for the treatment of thyroid cancer and patients should ask their doctor about whether testing is appropriate.
Stages of Thyroid Cancer
Stage I-II: Stage I-II thyroid cancers are generally confined to the thyroid, but may include multiple sites of cancer within the thyroid. Thyroid cancer that has spread to nearby lymph nodes is still considered to be in stage I-II when the patient is younger than 45 years of age as the presence of cancer in the lymph nodes does not worsen the prognosis for these younger patients.
Stage III: Stage III thyroid cancer is greater than 4 cm in diameter and is limited to the thyroid or may have minimal spread outside the thyroid. Lymph nodes near the trachea may be affected. Stage III thyroid cancer that has spread to adjacent cervical (neck) tissue or nearby blood vessels has a worse prognosis than cancer confined to the thyroid. However, lymph node metastases do not worsen the prognosis for patients younger than 45 years.
Stage III: thyroid cancer is also referred to as locally advanced disease.
Stage IV: Stage IV thyroid cancer has spread beyond the thyroid to the soft tissues of the neck, lymph nodes in the neck, or distant locations in the body. The lungs and bone are the most frequent sites of distant spread. Papillary carcinoma more frequently spreads to regional lymph nodes than to distant sites. Follicular carcinoma is more likely to invade blood vessels and spread to distant locations.
Recurrent: Thyroid cancer that has recurred after treatment or progressed with treatment is called recurrent disease.
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