Thyroid cancer accounted for 3.0% of all new cancer cases in Hong Kong
In 2019, there were 1 059 new cases of thyroid cancer that accounted for 3.0% of all new cancer cases in Hong Kong. The crude annual incidence rate of cancer per 100 000 Hong Kong population was 14. Women have a higher chance of getting the cancer and the female to male ratio was about 3.5 to 1.
The development of thyroid cancer is slow
It may take a few years for the cancer cells to develop into an obvious mass. With current technology, doctors can detect thyroid cancer even when it is small and the new treatments can achieve a high cure rate. However, as the cancer develops slowly, there is still chance of recurrence within a number of years after the initial treatment. Therefore, regular follow-up is advised.
What is Thyroid Cancer?
Thyroid is a gland in front of the neck beneath the voice box. It looks like a butterfly. It is an endocrine tissue which is responsible for the production of thyroxine. Situated behind the thyroid gland are parathyroid glands which secrete parathyroid hormone. Thyroxine is needed to keep the body functioning and its action affects blood sugar level, heart beat and kidney function. Parathyroid hormone helps regulate body calcium level. If cells in thyroid gland grow abnormally and they do not die as usual, cancer will be formed.
Thyroid cancer can be classified into 4 types:
- Papillary thyroid cancer: This is the most common type and it often occurs in young females.
- Follicular thyroid cancer: This is the next common type and it occurs mostly in older people.
- Medullary thyroid cancer: This is a rare type and it is likely to run in families.
- Anaplastic thyroid cancer: This is also a rare type and this usually occurs in people over 60 years old. It grows quickly and is difficult to cure. Improperly treated papillary thyroid cancer may transform into this type of cancer.
Apart from these types of cancer, non-Hodgkin’s lymphoma can rarely occur in thyroid.
Who have higher chance of having Thyroid Cancer?
The exact cause of thyroid cancer in most patients is unknown. The following are risk factors that can increase the chance of developing thyroid cancer.
Exposure to high level of radiation: This may be due to radiation therapy given in childhood or to unusually high level of radiation in the environment. Radiation leak from nuclear plant occurred before and there was a higher rate of thyroid cancer for the residents living near the nuclear plant.
Hereditary conditions: If a family member has had goiter, familial medullary thyroid cancer, multiple endocrine neoplasia or familial adenomatous polyposis, one has a higher chance of developing thyroid cancer.
Personal history: When one has had conditions like goiter and benign thyroid nodules, one has a higher chance of developing the disease.
- Sex: Females have a higher chance of having the cancer.
- Diet: Lack of iodine may lead to the development of thyroid cancer.
- Age: Many of the thyroid cancer patients are over 40 years of age.
What are the symptoms of Thyroid Cancer?
The commonly seen symptoms of thyroid cancer are the following:
- A painless lump in the neck with gradual increase in size.
- Persistent hoarseness.
- Pain in the neck or in the throat, and sometimes up to the ears.
- Having trouble on swallowing or breathing.
- Persistent cough but without flu symptoms.
Early thyroid cancer is not obvious and you may not be aware of its existence. To avoid delay in diagnosis and treatment, one should seek advice from a doctor when one worries about having a thyroid problem.
Prevention of Thyroid Cancer
The causes of thyroid cancer are not fully understood. There are some recognised risk factors of developing thyroid cancer, including:
Exposure to significant level of ionising radiation (including exposure to radiation fallout and history of radiation therapy to head, neck or chest in infancy/ childhood); Family history of thyroid cancer.
What are the treatments for Thyroid Cancer?
Most people with thyroid cancer will have surgery. The surgeon removes the whole thyroid gland or part of it, depending on the patient’s conditions. During the operation, surgeon will examine the lymph nodes close to the thyroid to see if they have been affected by cancer cells. If cancer has spread outside the gland, surgeon will remove the neighboring tissues as well.
After removal of entire or nearly all thyroid gland, patient needs to take thyroid hormone as replacement for the rest of his/her life. This also helps suppress the secretion of thyroid stimulating hormone (TSH). If the level of thyroid stimulating hormone is high, the remaining cancer cells may be stimulated, resulting in recurrence of cancer.
2. Radioactive iodine therapy
3. External radiation therapy
Should cancer cells still remain in the neck after the operation or the cancer cannot be removed by surgery, external radiation therapy is considered. This type of treatment is more commonly used in patients suffering from medullary thyroid cancer or anaplastic thyroid cancer. Another indication for this therapy is recurrence of cancer in the neck.
Prior to the therapy, a transparent mask which fits the patient’s head and neck is prepared. This mask helps immobilize the head during the therapy.
4. Targeted therapy
What are the complications of Thyroid Cancer?
After removal of the thyroid gland, patient may experience the following side effects:
- Bleeding, wound infection.
- Removal of parathyroid glands may result in drastic fall of calcium level inside the body, which causes limb numbness or cramps. Patient can take calcium tablets or vitamin D as supplement.
- A scar is left at lower part of neck after the operation but it will gradually fade out.
Potential risk and complications of surgical treatment for thyroid cancer includes:
- Anaesthetic complications and complications caused by pre-existing diseases.
- Systemic life-threatening complications including myocardial infarction, cerebral vascular accident, deep vein thrombosis and pulmonary embolism.
- Recurrent laryngeal nerve injury with aspiration and hoarseness in unilateral injury or airway obstruction in bilateral injury.
- Parathyroid insufficiency.
- Thyroid insufficiency requiring lifelong thyroxine replacement.
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