Thyroid cancer: Papillary Thyroid Cancer (PTC)
Papillary thyroid cancer is the most common type of thyroid cancer making up to 70-80% of all thyroid cancer cases. Papillary thyroid cancer can occur at any age, and its incidence has been increasing over the last few decades. There are about 20,000 new cases of papillary thyroid cancer in the United States each year. It is now ranked as the 8th most common cancer in women in the United States, and the most common cancer in women under the age of 25 years. Being diagnosed with papillary thyroid cancer can be very scary at first, however papillary thyroid cancers are most often slow growing tumors, and most can be removed surgically. Although slow-growing, papillary thyroid cancer can sometimes spread to the lymph nodes in the neck. Unlike some other tumors, positive lymph nodes do not usually worsen the generally excellent prognosis for. The involved lymph nodes can be surgically removed along with the thyroid. Most people diagnosed with PTC will not die from it.
Most patients with thyroid cancer do not have any symptoms. Typically, patients present with a thyroid nodule that is found to be cancer on further evaluation. 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 PTC
For most patients, we do not know the specific reason why they develop thyroid cancer, though it does appear to be more common in women, and is definitely seen in younger patients as well. 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 papillary 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.
Papillary thyroid cancer can run in the family and may be associated with genetic syndromes. Although rare, PTCPTC - papillary thyroid cancer can also be associated with goiters or colonic tumors. Therefore, patients should ask their relatives for a family history of papillary thyroid cancer, goiterGoiter - enlarged thyroid, colon/rectal tumors, or breast cancer. Patients with a positive family history are more at risk for thyroid cancer than those with no family history.
4. Diagnosing PTC
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. Papillary cancer cells are fairly straightforward to diagnose under the microscope. A result of PTCPTC - papillary thyroid cancer on FNA biopsy is about 95-98% accurate. Some centers may perform special stains or molecular studies on these cells to help determine if they are in fact cancerous.
Blood tests Most patients with papillary thyroid cancer have normal blood tests and thyroid function tests. Rarely, patients with PTC 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 papillary thyroid cancers make thyroglobulin, but not all do.
Genetic Testing In some familial cases of papillary thyroid cancer, genetic testing is necessary. No specific genes have been identified yet for PTC.
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.
5. Treatment of PTC
If you have a diagnosis of papillary cancer of the thyroid, surgery is almost always recommended as the first step. (See Thyroid Surgery) A total thyroidectomyTotal thyroidectomy - removal of the whole thyroid (i.e. removing the whole thyroid) is the best treatment for most cases of papillary cancer because:
- PTCPTC - papillary thyroid cancer tends to be multifocal (i.e. in multiple parts of the thyroid)
- RAI ablationRAI ablation - the use of radioactive iodine to destroy thyroid cells (either benign or cancer) post-operatively is more effective if there is no remaining normal thyroid tissue. RAIRAI - radioactive iodine will be mostly absorbed by any remaining normal thyroid tissue and may not make it to cancer cells
- Thyroglobulin is more effective as a tumor marker after total thyroidectomy. Once the thyroid is removed and RAI is given, the thyroglobulin level should drop to nearly zero. If the thyroglobulin levels rise above zero, then it is likely that the cancer is recurring (i.e. coming back). However, if there is any remaining normal thyroid tissue left, the thyroglobulin will not be close to zero and if the levels go up, it will be hard to determine if it is from cancer recurrence or if the normal thyroid is growing
- Studies have shown that patients who have had a total thyroidectomy have a lower chance of recurrence (i.e. cancer that comes back) in the neck
If the papillary cancer is very small (less than 1 cm) and limited to one side of the thyroid, some surgeons may only remove one half of the thyroid by performing a thyroid lobectomyLobectomy - removal of half the thyroid. This recommendation is not common because a total thyroidectomy is generally preferred. In cases where a PTC is discovered after only half the thyroid is removed, it may be necessary to perform a second operation soon after to remove the remaining thyroid gland (completion thyroidectomy). The type of thyroid surgery needed will be made with your surgeon and depends on certain factors such as your 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.
Papillary thyroid cancer can 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 (RAI) 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 ablation 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)
Other treatments Very few patients with papillary 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.