Thyroid cancer: Follicular/Hurthle Cell Cancer
Follicular and Hurthle cell cancers are two different types of cancer, but they are often considered in the same category. Together, these cancers are the second most common thyroid cancer, after papillary cancer. They can occur at any age, but are more likely in older people. These cancers can be hard to diagnose on FNAFNA - fine needle aspiration biopsy biopsy because although the cells look "funny" or abnormal, there is nothing about the individual cells that are definitive for cancer (unlike PTCPTC - papillary thyroid cancer where the cells have a very classic appearance). In cases of follicular and Hurthle cell lesions, the only way to tell if it is a cancer is look at the capsule surrounding the nodule and see if there is invasion (i.e. growth) outside the nodule. Follicular thyroid cancer does not tend to spread to lymph nodes, but rather spreads through blood vessels to other organs, such as the lungs and bones. Hurthle cell cancers, on the other hand, will sometimes spread to lymph nodes in the neck region, but less commonly than papillary thyroid cancer.
2. Symptoms and signs
Most patients with thyroid cancer do not have any symptoms. Typically, patients present with a thyroid nodule that on further evaluation is found to be cancer. As with all thyroid disease, a thorough history is important, such as a family history of thyroid cancer, personal history of radiation exposure, or enlarged lymph nodes. Your physician will review with you any symptoms such as pain, swelling in the neck, difficulty with swallowing, shortness of breath, difficulty with breathing or changes in your voice. If the nodule is large, it may cause symptoms such as difficulty swallowing, choking sensations, or a large mass in the neck. Rarely, the cancer can grow into the nerves (i.e. the recurrent laryngeal nerves) that control the voicebox and cause hoarseness.
3. Risk factors
For most patients, we do not know the specific reason why they develop thyroid cancer. It is important to note that some patients with multiple risk factors never develop thyroid cancer. In fact, most people who have thyroid cancer have no obvious known risk factor. Known risk factors for follicular and Hurthle cell thyroid cancer include:
Papillary thyroid cancer is more common in people who have a history of exposure to significant ionizing radiation. Radiation induced thyroid cancer can happen at anytime between a few years after exposure to as long as 30 to 50 years later. Radiation exposure is broken down into three major categories:
X-ray treatments were widely used in the 1940s and 1950s. This radiation was used to treat acne, enlarged tonsils, lymphomas, ringworm, enlarged thymus glands, and other ailments. X-rays were also used to measure foot sizes in shoe stores, and many people fondly remember seeing their "glowing green feet" and playing in these shoe fluoroscopes for hours while siblings were fitted for shoes. Children, younger than 15 years old, are most sensitive to radioactive damage to their thyroids.
Radiation therapy to the head, neck, and upper chest are an increasingly common cause of radiation induced thyroid cancer. Lymphoma, head and neck cancers, lung cancer, and breast cancer are some of the more common cancers that are associated with radiation exposure to the thyroid.
Thyroid cancer can be caused by radioactivity released from nuclear incidents such as the 1986 nuclear accident at the Chernobyl power plant in Russia. Many of the children in areas of Russia and the Eastern Block countries were inadvertently exposed to radiation and went on to develop thyroid cancer. Some people may also be exposed to radiation at work. However, routine X-ray exposure (for example dental X-rays, chest X-rays, mammograms) have NOT been shown to cause thyroid cancer.
Severe and prolonged iodine deficiency tends to increase the risk of developing follicular cancer. Iodine deficiency is not common in the United States or most of Europe.
There are several tests used to evaluate and diagnose a thyroid nodule suspicious for cancer. These tests include:
Ultrasound A thyroid ultrasound is a non-invasive imaging study in which sound waves are used to see an accurate picture of the thyroid gland as well as any enlarged lymph nodes. The ultrasound can tell the nodule's size, exact location, and whether it is solid or fluid-filled (i.e. cystic). An ultrasound cannot differentiate between cancer and benign tumors, but there are certain things that suggest cancer such as hypoechoic nodules with increased vascularity (i.e. blood vessels), microscopic calcium deposits (i.e. microcalcifications), and irregular borders. An ultrasound is also useful to evaluate any enlarged lymph nodes. If suspicious or large lymph nodes are seen, they can be tested with a FNAFNA - fine needle aspiration biopsy biopsy. For patients with a diagnosis of cancer, a full neck ultrasound looking specifically for enlarged lymph nodes (i.e. lymph node mapping) should be performed prior to any surgery.
Fine needle aspiration (FNA) FNA biopsy is the most accurate test for evaluating thyroid nodules. The biopsy may be performed under ultrasound guidance. A very thin needle is guided into the thyroid nodule and a small sampling of cells is aspirated or sucked into the needle. These cells are then examined under a microscope by a cytologist. An experienced thyroid cytologist is important to increase the accuracy of diagnosis. In cases of follicular neoplasmFollicular neoplasm - follicular cell tumor (benign or malignant) or Hurthle cell neoplasmHurthle cell neoplasm - variant of follicular neoplasm, the cells look abnormal, but the only way to make a diagnosis of cancer is to remove the thyroid lobe with the nodule and look at it under the microscope to see if there is invasion or growth outside of the nodule. There is about 15 to 25% chance that a follicular or Hurthle cell neoplasmNeoplasm - tumor that can be either benign or malignant is a cancer. The size of the nodule also plays a role in the risk of malignancy, especially for Hurthle cell neoplasm, where a larger nodule is more worrisome. Some physicians recommend treating any Hurthle cell neoplasm or nodule over 3.5 to 4cm as a cancer. Older patients and men are also more likely to have a follicular or Hurthle cell cancer than younger women.
Blood tests Most patients with follicular and Hurthle cell thyroid cancer have normal blood tests and thyroid function tests. Rarely, patients will have abnormal thyroid hormone levels and therefore, blood tests measuring levels of thyroid hormone (free T4T4 - thyroxine thyroid hormone and free T3) and thyroid stimulating hormone (TSHTSH - Thyroid stimulating hormone; also known as thyrotropin. The hormone that causes the thyroid to make and release thyroid hormone) may still be performed. Thyroglobulin levels are tumor markers (i.e. a blood test used to determine if the cancer has spread or come back). (See Thyroid Tests) Thyroglobulin levels in the blood may be measured in patients with known cancers after removal of the thyroid. Most follicular and Hurthle cell thyroid cancers make thyroglobulin, but not all do.
Genetic Testing No specific genes have been identified yet for follicular or Hurthle cell thyroid cancer.
Thyroid uptake scanThyroid uptake scan - radioactive iodine scan to detect hyperfunctioning thyroid nodules A RAIRAI - radioactive iodine thyroid scan can be performed to see if the thyroid nodule is functioning (a hot nodule) or non-functioning (cold nodule). Most hot nodules (97%) are benign and while cold nodules are more likely malignant, the chance of a cold nodule containing cancer is only about 10%. In general, FNA biopsy is more accurate and has replaced RAI scans in the work-up of thyroid cancer.
Magnetic resonance imaging (MRI), Computed Tomography (CTCT - computed tomography scan; special imaging to get a better picture of the anatomy scan) or Positron Emission Tomography (PETCT) scans These advanced imaging tests may be needed to see if large cancers are invading (i.e. growing into) or in close proximity to the large vital structures in the neck. They can also be used to identify involved lymph nodes, spread, or recurrence.
The best treatment for follicular and Hurthle cell cancers is total thyroidectomyTotal thyroidectomy - removal of the whole thyroid (i.e. removal of the whole thyroid). However, most of these patients will present with a follicular or Hurthle cell neoplasm. Therefore, most patients are initially treated with a thyroid lobectomyLobectomy - removal of half the thyroid to remove the nodule and make a diagnosis. (See Thyroid Surgery) If there is no evidence of invasion outside of the nodule, then it is a benign adenoma. However, if the cells grow outside of the surrounding capsule (capsular invasion), into blood vessels (vascular invasion), or into the lymphatics (lymphatic invasion), then the patient has cancer and usually needs to have the rest of the thyroid removed in an operation called a completion thyroidectomyCompletion thyroidectomy - when a lobectomy is performed and the pathology comes back that the lobe had cancer, the remaining lobe is surgically removed as well.. This can be done at any point after the first operation, but most surgeons prefer to either do it within a week or after 6 weeks.
If the cancer is very small and found only one side of your thyroid, or there is only a small amount of capsular invasion, without any evidence of vascular or lymphatic invasion, it may not be necessary to remove the rest of the thyroid. This decision will be made with your surgeon and medical doctors and depends on certain factors such as age, gender, size of the thyroid cancer, location of the cancer, and existence of enlarged or suspicious lymph nodes in the neck.
After total thyroidectomy, patients need to take thyroid hormone replacement pills for the rest of their life. Patients with thyroid cancer, who do undergo a lobectomy, and have only half of their thyroid removed, may still need to take thyroid hormone after surgery. The goal is to suppress or remove any stimulus for remaining thyroid cells to grow. TSHTSH - Thyroid stimulating hormone; also known as thyrotropin. The hormone that causes the thyroid to make and release thyroid hormone or thyroid stimulating hormone is the main signal that tells thyroid cells to grow and multiply. Giving a slightly higher dose of thyroid hormone than normal decreases TSH. The starting dose for levothyroxine for patients with cancer is approximately 2 mcg/kg.
Some Hurthle cell thyroid cancers will spread to lymph nodes in the neck. They may be felt pre-operatively on examination or seen on ultrasound. On ultrasound, the diseased lymph nodes may be bigger than normal, of unusual shape, or contain calcifications. The lymph nodes can be biopsied by FNAFNA - fine needle aspiration biopsy if they look suspicious. Removal of these lymph nodes is needed if the thyroid cancer is proven to have spread to them. This is called a lymph node dissection. (See Thyroid Surgery)
Radioactive iodine (RAIRAI - radioactive iodine) Thyroid cells normally take up iodine from the bloodstream and use it to produce thyroid hormone. In general, there are no other cells in the body that have the ability to concentrate iodine. Once the thyroid has been removed, RAI ablationRAI ablation - the use of radioactive iodine to destroy thyroid cells (either benign or cancer) therapy may be used to reduce the chance of the cancer coming back and to destroy any remaining thyroid cells (called remnant ablation). (See Radioactive Iodine) Hurthle cell cancers tend not to take up RAI as well as other cancers, but some do. The decision to use or not use RAI ablation for patients with Hurthle cell cancers will be made with your surgeon and medical team.
Other treatments Very few patients with thyroid cancer need external beam radiation or chemotherapy. These treatments are usually only used for very advanced or severe disease. These large cancers may have grown into important neighboring structures which cannot be safely removed, or are very bulky, or have spread to nonsurgically treatable areas (metastasesMetastases - spread of cancer). These treatments are used as a palliative measure to control the growth of the disease, and not to cure it.