Thyroid Cancer

Thyroid cancer is not common in Hong Kong, and the death rate is relatively low. According to data of Hong Kong Cancer Registry, there were 795 new cases (147 being males and 648 being females) and 44 deaths in 2014. Thyroid cancer usually affects middle-aged or older people but papillary cancer can occur in younger people. Women have a higher chance of getting the cancer and it is rarely seen in children.

The development of thyroid cancer is slow and 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 a number of years after the initial treatment. Therefore, regular follow-up is advised.

(Special thanks to Dr. C. K. KWAN, Consultant, Department of Oncology, United Christian Hospital for reviewing the information of this page)

1

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.

2

Thyroid cancer can be classified into 4 types:

  1. Papillary thyroid cancer: This is the most common type and it often occurs in young females.
  2. Follicular thyroid cancer: This is the next common type and it occurs mostly in older people.
  3. Medullary thyroid cancer: This is a rare type and it is likely to run in families.
  4. 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.

3

As the cause of thyroid cancer is largely unknown, there is no preventive measure. You should be alert if a family member has got thyroid cancer or a thyroid problem. It is best to have a self-check on the neck semi-annually and to have regular ultrasound scan.

4

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.
5

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.
 

6

Blood tests:
Samples of blood will be taken to check thyroid hormone and TSH levels. The blood will also be tested to check one's general health.

Fine-needle aspiration or biopsy:
Using a small needle, a sample of cells is taken out of a thyroid nodule and is examined under a microscope to check if there are cancer cells present. The doctor may use an ultrasound scanner to help guide the needle to the right area.

Surgical biopsy:
If a diagnosis can't be made after fine-needle aspiration, a doctor will make a small cut close to thyroid and extract a sample of tissue.

Ultrasound thyroid scan:
The doctor makes use of ultrasound scanner to create a picture of the neck and the inside of the thyroid gland. Hence, one can learn if the nodules are solid or filled with fluid.

Thyroid radioisotope scan:
A small amount of radioactive iodine is injected into a vein in the arm. After 20 minutes, the patient will lie on the bed and a gamma camera will be positioned over patient’s neck to measure the radiation activity of the patient’s thyroid gland. Cancer cells do not absorb radioactive iodine as good as normal thyroid cells. Therefore, the image will show the position of the cancer.

CT Scan:
CT scan is a series of x-rays which build up a three-dimensional picture of the inside of the body. Thus, the size and position of the tumor can be clearly displayed. Should the patient have history of iodine allergy or asthma he/she has to tell the medical staff beforehand.

7

(1) Surgery
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
Following the operation, treatment using radioactive iodine is considered if the cancer cells have not been completely eliminated or the cancer cells have spread to other parts of the body. This is one kind of internal radiotherapy. The radioactive substance is taken as a capsule or a drink. The thyroid cancer cells will absorb the radioactive iodine which will destroy them. Normal cells will remain unaffected.
Within 4 weeks before radioactive iodine therapy, patient should stop taking thyroid hormone because it will render radioactive iodine ineffective. He/She may be treated with recombinant human thyroid stimulating hormone (rhTSH) to overcome the potential problems of stopping thyroid hormone. Furthermore, patient should avoid food with high level of iodine, starting to do so at least 2 weeks prior to the therapy. The food include seafood, iodine-added salt, cough medicines, eggs, cheese and milk.
Within first 4 to 5 days after the therapy, high level of radiation can be detected in urine, blood, saliva and sweat. Patient will stay in hospital to avoid contacting other people. When the radiation level drops to the safety level, the patient can then be discharged.
Radioactive iodine therapy does not entail long term influence and female patients can have normal pregnancy. However, within 1 year after the therapy, a female patient is not recommended to become pregnant or to breastfeed a baby.

(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. The whole course of treatment usually takes 6 – 7 weeks.

(4) Targeted therapy
This is used when other treatments like surgery or radioactive iodine are no longer effective.
 

8

After removal of the thyroid gland, patient may experience the following side effects:

  • Bleeding, wound infection
  • Hoarseness
  • Fatigue
  • 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.

 
After receiving radioactive iodine therapy, the following side effects may occur:

  • Nausea
  • Dry mouth
  • Dry eyes
  • Swelling and tenderness of salivary glands
  • Change of taste or smell
  • Sore neck or upper chest

 
On receiving external radiation therapy, the following side effects may be present:

  • Nausea, fatigue
  • Sore throat, difficulty in swallowing
  • Dry mouth
  • Sore skin
  • Hoarseness

Most of the side effects are temporary. Should the patient feel uncomfortable, he/she can seek advice from doctor.

9

1. Care after surgery:
After surgery, patient should try to get out of the bed at the earliest possible time. If he/she needs to stay in bed, he/she should follow medical staff's instructions to maintain sufficient movement and to take deep breaths. For a better airway, he/she should be in a recumbent position when lying on bed. Patient may feel pain on swallowing and he/she may take fluid or soft food.

2. Regular medication:
Take medications (e.g. thyroxine hormone, calcium and vitamin D) according to doctor’s instructions

3. Regular followup:
Regular follow-up is vital in the early detection of cancer recurrence. Even though the thyroid gland has been removed, there is still chance of recurrence. Half a year after radioactive iodine therapy, a whole body scan may be done to see if cancer cells remain in the body. Thereafter, regular body checkup and blood test for thyroglobulin level will be done.

4. Adequate nutrition
Because of the side effects of the therapy, a patient may not tolerate normal diet and he/she can replace meals with nutritious, high-calorie drinks.

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