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Thyroid Cancer

In 2020, there were 978 new cases of thyroid cancer that accounted for 2.9% of all new cancer cases in Hong Kong. The crude annual incidence rate of cancer per 100 000 Hong Kong population was 13. Women have a higher chance of getting the cancer and the female to male ratio was about 3.8 to 1.

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 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.


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.


Asymptomatic individuals at average risk

Currently, screening for thyroid cancer is not recommended for asymptomatic persons at average risk.

Increased risk individuals

Persons at increased risk, including those with a history of head or neck irradiation in infancy or childhood, familial thyroid cancer or family history of multiple endocrine neoplasia type 2, should consider seeking advice from doctors regarding the need for and approach of screening.

How to investigate and make diagnosis for Thyroid Cancer?

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    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.

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    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. The tissue will be examined under a microscope to check if there are cancer cells present.

    Patients should provide information concerning the current medications used especially antiplatelet and anticoagulation drugs and any allergic history. In patients using anticoagulation and antiplatelet drugs, they may need to stop or modify the dosage of the medications.

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    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.

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    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.

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What are the treatments for Thyroid Cancer?

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    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.

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    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.

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What are the complications of Thyroid Cancer?

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.

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.
  • Bleeding.
  • Infection.

How do patients with Thyroid Cancer take care of themselves?

  1. Care after surgery

    After surgery, patient should try to get out of the bed at the earliest possible time. If patient needs to stay in bed, patient should follow medical staff's instructions to maintain sufficient movement and to take deep breaths. For a better airway, patient should be in a recumbent position when lying on bed. Patient may feel pain on swallowing and patient 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 follow-up

    Even though the thyroid gland has been removed, there is still chance of recurrence. Therefore, regular follow-up is vital in the early detection of cancer 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 patient can replace meals with nutritious, high-calorie drinks.


Radioactive Iodine for Thyroid Cancer

  1. Introduction

    Radioactive iodine is a form of iodine that emits radiation. When it is absorbed by the body, it will be concentrated in thyroid tissue. The radiation given off will destroy any remaining thyroid cells that may have escaped surgical removal. This reduces the risk of tumour recurrence and facilitates detection of early relapse by blood tests. It can also be used to treat cancer that has returned and still achieve a cure.

    Radioactive iodine is taken by mouth in liquid or pill form. Most of the radioactivity is absorbed by thyroid tissue. Any radioactivity not collected by thyroid tissue will be eliminated within a few days through urine, faeces, saliva and sweat. Other organs in the body will receive some incidental radiation during this time, but this small amount of radiation typically does not produce any adverse effect.

  2. Preparation before the treatment

    The following preparation ensures good absorption of radioactive iodine. Please refer to the instruction sheet given for the exact dates.

    • Before radioactive iodine, avoid iodine-containing contrast agents used in X-ray or CT scans. Please ask the doctor if in doubt.
    • Stop taking thyroxine tablets 3 to 4 weeks before radioactive iodine (unless THYROGEN injection have been instructed otherwise). During this period, patient may experience symptoms like fatigue, low mood and poor concentration. This is normal and will disappear once patient start taking thyroxine again.
    • Having a low iodine diet 2 weeks before radioactive iodine. Avoid all seafood (e.g. fish, shrimps, crabs, shellfish, seaweed, oyster sauce), sea salt, dietary supplements containing iodine, as well as iodine-containing medications (e.g. iodine-containing cough medicine).
    • Notes:
      • Radioactive substance can cause teratogenicity. Male and female patients should take contraceptive measures for a period of time as instructed by your doctor
      • Female patients should avoid breastfeeding for a period of time before and after the radioactive iodine treatment as instructed by your doctor
      • Please tell the doctor if patient have previously received radioactive iodine in another hospital.
      • Please tell the doctor if patient had allergic reaction to iodine before.
      • Please tell the doctor if patient need to be in close contact (within 1 meter) with babies or young children.
  3. Treatment procedure

    • Please come at the scheduled time for the treatment.
    • Patient will stay in hospital for a few days (usually 2 days) after treatment to reduce other people’s exposure to radiation. During the hospital stay patient should remain in a designated room with the door closed. Patient may be asked to share the facility with another patient of the same sex who is having similar treatment. Since patient are radioactive, hospital staff will spend only short periods of time in the room. When they enter the room they may stand behind a lead screen and patient should try to remain on the opposite side of the screen.
    • To minimize radiation exposure, visitors are not encouraged. Visitors should stay behind the lead screen and keep the visit as short as possible. Pregnant women and children are not allowed as they are more sensitive to the effects of radiation.
    • Please maintain good personal hygiene and keep the room clean during the stay:
      • Drink plenty of fluids and make urinate more frequently. This will flush the excess radioactive iodine out of the body more rapidly.
      • Sweat is also radioactive. Shower daily and wear a hospital gown to avoid contamination of patient’s own clothes.
      • Please put all used eating utensils and garbage in the special plastic bag provided in the room.
      • Use only the designated toilet and keep it clean. Avoid splashing urine outside the toilet bowl or on its borders. Flush the toilet twice after each use. Wash your hands thoroughly each time you go to the toilet and rinse the sink after use.
    • Due to the stringent requirement on radiation protection, patient is not allowed to leave the designated room. Patient is also required to follow the instructions on radiation protection given by the medical staff. The discharge date depends on how quickly the radioactivity leaves the body. Medical staff will take radiation measurements and work out if the level is safe for discharge. If you feel unwell anytime during the treatment period, please inform medical staff.
  4. After the treatment

    • Patient’s radiation level will be measured on the day of discharge. Below are some guidelines to follow for a period (usually about one week) after the treatment. The exact duration to be instructed by your doctor:
      • Avoid being next to the same person for prolonged duration.
      • Sleep alone if possible and avoid sexual intercourse.
      • Avoid journeys on public transport for prolonged duration.
      • Avoid going to crowded places / places of entertainment.
      • It is safe to be in the same room with children or pregnant women, but do not sit next to them for prolonged periods, and avoid activities like hugging or kissing.
      • Do not return to work if prolonged close contact (i.e. within 1 metre) with other people is involved at work, especially children or pregnant women. Please inform medical staff if sick leave certificate is needed.
      • Drink plenty of fluids and empty your bladder frequently to flush the excess radioactive iodine out of the body more rapidly.
      • Keep the toilet clean. Avoid splashing urine outside the toilet bowl or on its borders. Flush the toilet twice after each use. Wash your hands thoroughly each time you go to the toilet and rinse the sink and bathtub after use.
      • Use separate eating utensils and wash them separately.
      • Do not share towels. Wash the towels and underclothing separately from other people’s clothing.
    • Refrain from seafood and thyroxine should be continued after radioactive iodine for a period of time as instructed by the doctor.
    • In the event of death, cremation may be denied by health authorities or may be deferred for a period of time depending on residual radioactivity.
  5. Risk and complication / side effects

    • Each patient reacts differently and may experience none, some, or all of the complications to a varying degree of intensity. Early / short term side effects may occur during treatment, but usually disappear within a few days to several weeks later.
      • Common Early / Short Term Side Effects:
        • Decreased appetite.
        • Nausea and sometimes vomiting. This can be reduced by not taking too much food on the day of treatment.
        • Dry mouth, changes in or temporary loss of taste sensation; discomfort, soreness or swelling of the mouth or throat. Drinking plenty of water helps to reduce these symptoms.
      • Uncommon Early / Short Term Side Effects:
        • Drop in blood counts which increases the chance of infection and bleeding.
        • Temporary hair loss.
        • Dry eyes.
        • Mild swelling or pain over the front of the lower neck.
        • Temporary loss of smell sensation.
        • Female may have disturbance in the menstrual cycle.
        • Male may have reduced sperm counts temporarily.
      • Rare Early / Short Term Side Effects:
        • Inflammation of the stomach causing indigestion, heartburn or ulcer.
        • Bladder inflammation with frequency and pain on urination.
        • If there is significant residual thyroid tissue after surgery, significant neck swelling or pain may occur. This can be prevented by taking steroid. Doctor will decide if this is necessary.
        • For patients with tumour spread to the brain, bones, spinal cord, or near major airways, tumour swelling or bleeding may occur.
        • For patients with diffuse tumour spread to the lungs, lung inflammation may occur with symptoms of dry cough, shortness of breath and / or low grade fever.
        • Allergic reaction resulting in skin rash, shortness of breath and drop in blood pressure. This is potentially life-threatening and may require resuscitation.
    • Radioactive Iodine treatment may also cause late / long-term side effects
      • Uncommon Late / Long Term Side Effects:
        • Dry mouth. This may predispose to dental caries and gum inflammation.
        • Permanent changes in, or loss of taste sensation.
        • Persistent discomfort, soreness or swelling of the mouth or throat.
        • Chronic dry eyes.
        • If patients have tumour spread to the lungs, it may lead to deterioration in lung function.
        • Repeated high dose radioactive iodine treatment in female may cause damage to the ovaries resulting in early menopause and infertility.
      • Radiation-induced tumours may occur, but this is extremely rare and mainly applies to cases of repeated high dose treatment.
    • Notes before treatment:
      • Radioactive iodine will not affect future fertility, except in rare cases of repeated high dose treatment.
      • The risk of abortion may be increased in female patients who become pregnant within 1 year after treatment.
      • On rare occasions, patients may develop severe life threatening complications due to radioactive iodine and die.
      • Despite all precautions, unexpected complications sometimes occur.
      • Serious side effects and complications are uncommon. Their chance of occurrence, clinical presentation and severity vary among patients because of individual differences in the dose of radioactive iodine received and tissue response to radiation. Medical staff will strive to ensure that every patient receives the most appropriate treatment with the least side effects.
      • It may be possible that the intended treatment outcome cannot be achieved, the disease may not be alleviated and it may recur or progress in the future.
      • Despite all precautions, unpredictable and unpreventable adverse outcomes may occur after treatment. Patient needs to fully understand the possible complications before deciding on undergoing the treatment.
  6. Follow-up arrangement

    • A follow-up appointment will be arranged to assess patient’s response to treatment and look out for complications. Please attend the appointment as scheduled and follow the instructions on taking medications strictly.
  7. Remarks

    For further information please contact your doctor.