Thyroid cancer refers to formation of malignant cells in the thyroid gland. Accumulation of these cells forms a cancerous growth in the thyroid which often takes the form of a nodule (thyroid nodule) at the beginning.
There are various types of thyroid cancer, named depending on group of cells affected:
- Papillarythyroid cancer– papillary thyroid cancer is the most common type of thyroid cancer; it affects mostly women aged between 30 and 40. Usually, papillary thyroid cancer grows slowly, and tends to have good prognosis when diagnosed early. The tumor develops in the cells that produce the triiodothyronine, one of the thyroid hormones.
- Follicular Thyroid Cancer– this type of thyroid cancer, although a little slow growing, tends to grow quicker than papillary carcinoma. It occurs mostly in women, principally women over 50 years old. Prognosis of follicular cancers is not alarming when diagnosed and treated early. Usually, follicular thyroid cancers develop in the cells of the thyroid gland that produce and secrete thyroxine (thyroid epithelial cells, also called follicular cellsor principal cells).
- Medullary Thyroid Cancer– this form of thyroid cancer is more aggressive than papillary and follicular cancers; it has poor prognosis. It tends to spread to distant organs in the body: liver, bone, brain, and adrenal medulla. Medullary cancer usually begins in the parafollicular cells (or C cells). This group of thyroid cells produces and secretes calcitonin, an hormone that acts by keeping the blood calcium at normal levels. About 25 percent of medullary thyroid cancer is due to genetic disorders.
- Anaplastic thyroid cancer– unlike papillary carcinoma and follicular thyroid cancer, anaplastic thyroid cancer is a very life-threatening condition; it tends to grow rapidly, and resist to treatments. Due to its metastatic characteristic, anaplastic thyroid cancer has a very poor prognosis. Usually, the tumor begins in the follicular cells of the thyroid, and affects most often people aged 60 and over. Anaplastic thyroid cancer is rare, representing about 3% of all thyroid cancers.
- Thyroid lymphoma– this is a very rare form of thyroid cancer. Usually, the cancer begins in the immune system cells of the thyroid (lymphoma cells). Development of thyroid lymphomais often associated with preexisting chronic autoimmune disease of the thyroid gland called thyroiditis (inflammation of the thyroidgland).
Thyroid Cancer Incidence
Although thyroid cancer is rare, its incidence has dramatically increased over the last two decades. Worldwide, the annual incidence rate ranges from 0.5 to 10 cases per 100,000 people. In the United States, over the 11 year period, between 1997 and 2007, the incidence of thyroid cancer approximately doubled from 16,100 to 33,550 per year. According to the National Cancer Institute, It is estimated that 10,000 men and 27,200 women were diagnosed with thyroid cancer in 2009; 1,630 people died of it.
From 2002-2006, the median age at diagnosis for cancer of the thyroid was 48 years of age. Percentages and ages of people diagnosed with thyroid cancer during that period were approximately:
- 8% under age 20;
- 9% between 20 and 34;
- 0% between 35 and 44;
- 8% between 45 and 54;
- 9% between 55 and 64;
- 1% between 65 and 74;
- 2% between 75 and 84;
- 4% 85+ years of age.
Thyroid Cancer Causes
The thyroid is butterfly-shaped organ located in the lower neck, below the larynx. It has two cone-like lobes connected by a tissue called isthmus. In response to the hypophysis (an important gland of the endocrine system located at the base of the brain), through the thyrotropin (thyroid stimulating hormone), the thyroid secretes hormones used to monitor vital functions of the body. The two main thyroid hormones are thyroxine, a hormone containing iodine, which regulates the metabolism so it works normally; and calcitonin, a hormone that keeps calcium levels at normal levels.
All these functions are performed by thousands of cells working synergistically in the thyroid gland. Every day, by a natural process called self-cell destruction or apoptosis, thousands of these cells die to be replaced by new healthy cells. Thyroid cancer occurs when there is abnormal cell production and proliferation in the thyroid gland. The causes of this cellular disorder are not well known by scientists; however, several factors are suspected (see risk factors).
Thyroid Cancer Risk Factors
The main causative factors for thyroid cancer include:
- Age– thyroid cancer tends to affect especially people aged between 25 and 65; however, the median age at diagnosis is 48 years of age.
- Sex– women are more victim of thyroid cancer; the incidence is almost three times more in women than in men.
- Environment– living close to a nuclear power plant
- Family History of thyroid cancer– if you have a family history of medullary thyroid cancer, you are at greater risk than the rest of the population.
- Diet– persistent excess or deficiency of iodine in your diet may also contribute to the development of thyroid cancer.
- History of goiter– goiter is a non-cancerous inflammation of thyroid gland often due to iodine deficiency, however, chronic swelling in the thyroid gland can lead to thyroid cancer.
- Exposure to high levels of radiation– prolonged exposure to radioactive materials may also promote the development of thyroid cancer. If you have been undergoing radiation treatment to the head and neck, you may have exposed to high levels of radiation.
Thyroid Cancer Symptoms
Thyroid cancer can be completely asymptomatic for months or years. In most cases, the cancer grows very slowly without causing any apparent symptoms. As the tumor increases in size, you may notice presence of a nodule (a small mass) in your lower neck. In general, thyroid cancer can cause the following symptoms:
- lower front neckmass
- hoarse voice
- pain in the throat or neck
- difficulty breathing
- difficulty swallowing
- Swollen lymph nodes in your neck.
If you experience these symptoms, it does not mean you have thyroid cancer; in fact, about 5% of mass in the neck are cancerous. Therefore, if you notice a lump in your neck, consult your doctor before assuming anything.
Thyroid Cancer Complications
Although thyroid cancer has a good prognosis, the tumor can return after treatment, and becomes very life threatening. The cancer can also invade lymph nodes in the neck and distant sites of the body such as the lungs or bones.
In addition, surgical removal of the tumor in your neck can lead to irreversible complications:
- permanent paralysis of vocal cord;
- Hypoparathyroidism (lack of production of parathyroid hormone) – which can be due to decreased calcium levels in the blood (hypocalcemia).
Thyroid Cancer Diagnosis
Your doctor will ask you questions about your medical history and your family’s. The interrogation can give him an idea of your state of health, but not a confirmation of the diagnosis. In most cases, thyroid cancer diagnosis include physical exam, blood tests, imaging techniques and biopsy.
Physical exam – during the physical exam, your doctor will examine your throat in search of signs of thyroid cancer: lump in the neck, swollen lymph nodes, etc. However, even if he finds vivid signs of the disease, he cannot conclude you have thyroid cancer; these signs are simply indicators. Therefore, to confirm the diagnosis, he will perform other diagnostic procedures.
Neck ultrasound – this is an imaging technique allowing your doctor to confirm presence of a nodule that was suspected during the physical examination. Using the ultrasound, your physician can measure the size of the tumor and precisely locate it within the thyroid gland. In addition, using ultrasound, your physician may identify and compare isolated or associated nature of the nodule with other similar formations in order to rule out other medical conditions of the thyroid gland.
Blood test – this exam allows your doctor to determine the level of your thyroid stimulating hormone (TSH), which gives indirect information on the thyroid function. In addition, he will search for the level of calcitonin, a hormone secreted by certain cells of the thyroid gland in response to signals from the hypothalamus. The increase of calcitonin in blood concentration is a vivid marker of medullary thyroid cancer.
Needle biopsy – needle aspiration biopsy (NAB) is a technique consists of removing cells from your thyroid gland. The sample obtained is studied under microscope to look for cancer cells. This biopsy is the most reliable examination to distinguish cancerous nodules from benign nodules.
Scintigraphy – using this diagnostic procedure, a health care specialist can produce functional images of the thyroid gland to determine the size, shape and position of the thyroid gland. In general, the images are taken after ingestion of very low doses of radioactive marker. Once injected, the marker binds specifically to abnormal elements of the thyroid. Scintigraphy is indicated for the detection of abnormalities in the thyroid gland, including cancerous growth.
Thyroid Cancer Stages
Once the cancer is confirmed in your thyroid, your physician will determine its stage. Knowing the stage of the cancer, your doctor will be able to determine the most appropriate treatment to fight the disease. A thyroid cancer stage is determined based on the size of the tumor and whether it has spread beyond the thyroid gland. Since aggressivity of thyroid cancer varies from one type to another, there are two types of staging.
There are two stages for papillary thyroid cancer and follicular thyroid cancer in patients under 45 years:
- Stage I– to this point, the cancer has not spread to distant sites of the body, but it can be any size and may have spread to the neck, upper chest and/or to nearby lymph nodes.
- Stage II– at this stage, the cancer has not only invaded the chest and/or nearby lymph nodes but also other remote sites of the body such as bones or lungs.
There are four stages for papillary thyroid cancer, follicular thyroid cancer and medullary thyroid cancer in patients 45 years and older.
- Stage I– the cancer is limited to the thyroid gland, and measuring 2 cm or less in diameter.
- Stage II– the cancer is still limited to the thyroid, but has increased in size, usually between 2 and 4 cm in diameter;
- Stage III– at stage 3, the size of the tumor is more than 4 cm in diameter and can have been spread outside the thyroid and/or lymph nodes in the neck without evading distant organs of the body.
- Stage IV– the tumor can be at any size, and has extended beyond the thyroid capsule to reach the lymph nodes in the neck and upper chest and other body parts, such as lungs or bones.
Thyroid Cancer Treatment
Treatment of thyroid cancer involves a combination of surgery, hormone therapy, radioactive iodine (radioiodine) therapy, radiation therapy, and chemotherapy in case the case the cancer has spread.
Surgery is the best treatment for thyroid cancer. The most performed surgery in the treatment of thyroid cancer is thyroidectomy. During the procedure, your surgeon can remove part or the entire thyroid gland. Depending on the aggressiveness of the tumor, the thyroid and lymph nodes can be completely removed.
In some cases of thyroid cancer, the surgeon may also remove lymph nodes from your neck located near the thyroid to prevent the cancer from spreading. He can also do so to remove a tumor that has already spread into nearby lymph nodes.
After the surgery
Although surgery is often successful in combating thyroid cancer, it is not without side effects. The parathyroid glands can be damaged during surgery, and lead to calcium deficiency in your blood. In addition, your vocal cords may be affected, which usually leads to vocal cord paralysis, hoarseness, soft voice or difficulty breathing. However, these are rare and are often transient. The scar resulting from the operation is very discrete, even invisible.
Thyroid hormone therapy
Your thyroid gland being removed, you will have no thyroid hormones. To substitute your natural thyroid hormones, you will be prescribed a thyroid hormone replacement therapy; Levothyroxine Sodium (Synthroid, Levoxyl, Levothroid, Unithroid) are the most common drugs prescribed. This hormone replacement therapy should be taken daily, often for life. The drugs can maintain the TSH (pituitary hormone thyroid stimulating) to low levels to prevent growth of cancer cells. In most patients, these drugs improve quality of life and prevent the risk of complications.
Radioactive iodine (radioiodine) therapy
After the operation of thyroid cancer, you will be prescribed a radioactive iodine treatment to destroy or reduce cancerous cells remaining after the surgery. The therapy may also be recommended to treat recurring thyroid cancers. Radioactive iodine treatment is available in capsule or liquid form.
Before the treatment, you will be recommended to temporarily stop all thyroid hormone therapy, avoid medications containing iodine or perform radiological examinations using iodinated contrast agents. In addition, you should consume a diet low in iodine for 6 weeks, and avoid pregnancy if you are a woman.
The treatment may require hospitalization for 4 days to prevent other people from exposing to the radiation. In case, you are not hospitalized, you’ll need to take precautions to protect your family and friends from the radiation.
Side effects are often transitory, and may include:
- neck or/and chest pain
- dry mouth
- dry eyes
- Altertion of taste or smell.
External Radiation Therapy
External beam radiation can also be used in the treatment of thyroid cancer. During the therapy, high-energy rays pass through your skin into the tumor, thus destroying the cancer cells. In general, external radiotherapy does not require hospital stay or special care, unlike radioactive iodine (radioiodine) therapy. External radiation therapy is more often used in the treatment of medullary thyroid cancer and anaplastic thyroid cancer.
The therapy can destroy nearby healthy tissue along with the cancer cells, which can lead to several side effects:
- skin burn-related changes
- trouble swallowing
Chemotherapy involves administration of powerful chemical agents that act by preventing the reproduction or spread of cancer cells. However, chemotherapy is rarely used to treat patients with thyroid cancer. Unlike radiotherapy and surgery, chemotherapy attacks all cells in the entire organism that multiply quickly, which often causes side effects:
- loss of appetite
- hair loss
- Increased risk of infection.
Thyroid Cancer Prognosis
Although there are many forms of thyroid cancers, the most common types are papillary and follicular cancers. Fortunately, papillary and follicular are the most curable of thyroid cancers. When diagnosed early and treated appropriately, papillary and follicular thyroid cancers can have about 97% cure rate.
According to the National Cancer Institute (NCI), the overall 5-year relative survival rate for 1999-2005 from 17 SEER (Surveillance Epidemiology and Ends Research) geographic areas was 97.3%. Five-year relative survival rates by race and sex were:
- 8% for white men;
- 2% for white women;
- 4% for black men;
- 5% for black women.
Thyroid Cancer Prevention
Several factors can cause formation of cancerous cells in your body; fortunately, some of them can be prevented. To prevent thyroid cancer, you can take the following step:
Reduce your risk – if you have an inherited gene mutation that may increase the risk of thyroid cancer, talk to your doctor about a prophylactic thyroidectomy. In addition, if you live close to a nuclear power plant, talk to your doctor about medications that can block the effects of the radiation on your thyroid.
Other preventive methods –
- avoid exposure to high levels of radiation
- avoid excessive or persistent lack of iodine in your diet
- consult your doctor regularly if you have a history of goiter
- see your doctor regularly if you have a family history of medullary thyroid cancer
- keep your immune system
- use an air purifier if you live in an industrial or an high pollution environment
- stop smoking and avoid second-hand tobacco smoke;
- tell your doctor or dentist of any change in your oropharyngeal cavity that indicates cancer
- adopt a healthy diet – a diet contains 5 to 10 servings of fruits and vegetables a day may help reduce the risk of all types of cancer, including thyroid cancer.
- exercise regularly
- maintain a healthy weight
- limit your alcohol consumption;
- perform safe sex
- Reduce your exposure to ultraviolet (UV) radiation from the sun or artificial tanning devices, such as tanning beds.