The thyroid gland produces hormones which regulate body metabolism, heart rate, blood pressure, body temperature, and weight.
In 2012, the American Thyroid Association (ATA) noted that the incidence of thyroid cancer is increasing faster than any other cancer in the United States, and 56,000 people were expected to be diagnosed with thyroid cancer in that year.
In 2016, the American Cancer Society (ACS) expected this figure to be around 62,450 people. Of these, 49,350 are likely to be women, and 19,950 men.
Since the 1990s, the number of cases of thyroid cancer has tripled, but this is partly due to improved methods of screening and detection of asymptomatic cancers. In other words, improved technology is detecting more hidden cases.
Types of thyroid cancer
There are various types of thyroid cancer.
The thyroid gland is a butterfly-shaped gland that produces key hormones.
Papillary thyroid cancer accounts for about 80 percent of cases. It is most likely to appear in patients aged between 30 and 50 years of age. This type of cancer grows slowly, it is easy to treat, and it has a good prognosis.
Follicular thyroid cancer accounts for about 10 percent of cases, mostly in individuals aged 50 years or over. It more common in people from countries with inadequate dietary iodine intake. It is also associated with a good prognosis, but it is more likely to spread than the papillary type.
Medullary thyroid cancer accounts for about 4 percent of cases. This type is more aggressive than the papillary or follicular types, and it is more likely to spread to other organs. It can be due to a hereditary syndrome that is also associated with other endocrine disorders.
Hurhtle cell carcinoma, also called oxphil cell carcinoma, is a subtype of follicular and accounts for about 3 percent of thyroid cancers.
Anaplastic thyroid cancer is an aggressive cancer that spreads easily and accounts for about 2 percent of cases. It normally occurs patients aged over 60 years.
What is the thyroid gland?
The thyroid gland makes and stores hormones that control blood pressure, body temperature, heart rate, and metabolism. Metabolism is the process that converts food into energy. The function of every cell in the body depends on the hormones that the thyroid gland produces.
The thyroid gland lies in the lower, front part of the neck or below the "Adam's apple." It has a butterfly shape with two lobes, or "wings," attached to each other by a middle section.
The thyroid gland needs iodine to work properly and to produce the necessary hormones.
The thyroid gland has:
- Follicular cells, which produce thyroxine (T4) and triiodothyronine (T3). These two hormones affect heart rate, body temperature, and energy levels.
- C cells, which produce calcitonin. Calcitonin helps to control calcium levels in the blood. Calcium is necessary to make strong bones and to prevent blood clots.
Symptoms of thyroid cancer
Thyroid cancer normally develops very slowly, and symptoms do not usually appear during the early stages. Autopsy studies suggest a prevalence of between 5 percent and 30 percent of cases with no clinical symptoms. This makes it harder to diagnose at the treatable stages.
The first symptom to appear may be a small, painless lump in the neck, although not all such lumps are cancerous.
Later symptoms may include:
- Pain in the neck and throat
- Hoarseness, or problems speaking with a normal voice
- Swollen lymph nodes in the neck
- Breathing difficulties
Risk factors for thyroid cancer
A number of factors can increase the risk of developing thyroid cancer.
Radiation exposure, especially in early childhood, increases the risk of developing thyroid cancer.
The number of cases increased in the area of Chernobyl in the former Soviet Union, following nuclear fallout after a major nuclear explosion in 1986.
Thyroid cancer may also result from radiation treatment that was carried out as therapy at a time when radiation risks were not properly understood, specifically before the early 1960s.
Exposure to radiation increases the risk of thyroid cancer.
Low levels of radiation, for example as the result of medical and dental imaging tests, are unlikely to increase the risk, but thyroid shields are recommended in some cases.
According to the ATA, the risk of thyroid cancer from radiation exposure depends on how old the person is when they are exposed. The risk is higher in children, and the younger the child, the greater the risk. Higher doses also increase the risk. Radiation poses some risk to adults, they say but the risk is low.
The ATA recommend the use of shields to protect patients from radiation in some diagnostic tests. They also call for the use of radiation to be minimized in dental treatment, and for all patients to be informed about the potential risks of radiation.
Some health conditions or diseases can increase the risk. People with Hashimoto's thyroiditis, Cowden's syndrome, thyroid adenoma and familial adenomatous polyposis have a greater chance of developing thyroid cancer.
Genetic factors can increase the chance of developing medullary thyroid cancer. Around 25 percent of people who develop medullary thyroid cancer have an abnormal gene.
The American Cancer Society say that most people with thyroid cancer do not have a family history of the condition, but when a patient does have a close relative with the disease, they have a higher risk of developing it. Inherited faulty genes and other inherited conditions are thought to play a role.
Lack of iodine in the diet can increase the risk. In the United States, iodine is added to table salt, making a lack of iodine less likely.
How is thyroid cancer diagnosed?
The first step will be to examine the patient's neck and throat and to ask questions about the symptoms.
A blood test will measure thyroid function by assessing the levels of specific hormones in the blood.
High levels of thyroxine and triiodothyronine suggest an overactive thyroid gland, while raised levels of thyroid stimulating hormone (TSH) suggest that the thyroid gland is underactive. TSH is produced by the pituitary gland in order to stimulate the thyroid gland. Blood tests are not used to diagnose thyroid cancer but can tell if the thyroid if functioning properly.
Fine-needle aspiration cytology, or a biopsy, involves passing a small needle into the swelling in the patient's neck, to remove a sample of cells for examination under a microscope.
A biopsy will reveal whether a lump is cancerous, and, if so, what type of cancer it is.
If the results are inconclusive, a biopsy may be carried out surgically, to remove a small sample of the thyroid gland to see if it contains cancerous cells.
Treatment for thyroid cancer
Many cases of thyroid cancer can be treated and cured through surgery, radioactive iodine or radiotherapy, or a combination of these treatments.
Surgery is a treatment option for thyroid cancer.
Common types of surgery include:
- Thyroidectomy, the surgical removal of the thyroid gland. If cancer has moved to lymph nodes in the neck, the surgeon may also remove these.
- Lobectomy, or hemithyroidectomy, the surgical removal of one of the lobes of the thyroid gland.
Risks of surgery include bleeding, nerve injury, permanent, or temporary hoarseness, breathing problems and rarely the need for tracheotomy, infection and damage to the parathyroid glands.
If the parathyroid glands, which help regulate blood calcium levels, are damaged the patient may need to take calcium supplements. Usually, the parathyroid glands recover after some time.
Thyroid hormone therapy, in the form of hormone replacement medication, will be necessary, if the thyroid gland is completely or partially removed. The patient will need this treatment for the rest of their life, as well as regular blood tests to make sure the hormone levels are adequate.
Radioactive iodine therapy may be needed after surgery, to prevent the thyroid cancer from returning. The patient may need to follow a low-iodine diet two weeks prior to treatment with radioactive iodine. Pregnant women should not receive radioactive iodine treatment.
External radiation therapy, or radiotherapy, is normally only used for medullary or anaplastic thyroid cancers.
Chemotherapy is usually only used to treat anaplastic thyroid cancer that has metastasized, or spread to other parts of the body.
Newer treatments like targeted oral therapies can sometimes be used in later stage thyroid cancers when other treatments are no longer effective.
Prognosis for patients with thyroid cancer
Survival and recurrence rates depend on the type of thyroid cancer and the stage at diagnosis.
Patients with most types of thyroid cancer can expect a 100 percent 5-year survival rate, if their cancer is diagnosed in the early stages.
If papillary or follicular thyroid cancer are diagnosed in stage IV, the patient has around a 50 percent chance of survival over 5 years. For medullary thyroid cancer, the 5-year chance of survival is 28 percent.
Recent research suggests that despite increases in detection of thyroid cancer, rates of survival are not increasing.