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Prevalence of Thyroid Cancer in Hong Kong
In 2022, there were 1 049 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 3.6 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. According to the Cancer Registry statistics, the five-year relative survival rates were very high (>95%) for stage I to III. Stage IV thyroid cancer still had a five-year survival rate of 69%. 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.
Symptoms of Thyroid Cancer
The thyroid gland is shaped like a butterfly at the front of the neck below the throat. It is an endocrine tissue responsible for secreting thyroid hormones. Behind the thyroid gland are the parathyroid glands, which secrete parathyroid hormone. Thyroid hormones regulate metabolism, blood sugar, heart rate, and kidney function. In contrast, parathyroid hormone helps regulate calcium levels in the body, balances bone calcium, and promotes calcium absorption in the intestines and kidneys. When thyroid cells grow abnormally and uncontrollably, thyroid cancer develops.
Early symptoms of thyroid cancer are often not obvious and can easily be mistaken for other conditions. If any concerns arise, seeking medical attention for proper evaluation is essential to avoid delays in diagnosis and treatment.
Understanding Cancer Causes
The exact causes of thyroid cancer remain unclear, but the following risk factors may be associated with its development:
Common Diagnostic Methods
The diagnostic methods for thyroid cancer include:
In Hong Kong, up to 90% of thyroid cancers are well‑differentiated and have a good prognosis, namely the papillary and follicular subtypes.
| Type | Prevalence | Typical Patient Population |
|---|---|---|
| Papillary carcinoma | Most common | Young women |
| Follicular carcinoma | Less common | Elderly |
| Medullary carcinoma | Rare | Individuals with a hereditary family history |
| Anaplastic (undifferentiated) carcinoma | Rare | Elderly |
According to guidelines from the American Joint Committee on Cancer and the American Cancer Society, well-differentiated thyroid cancer is classified into 4 stages:
| Stage | Under 45 years old | Over 45 years old |
|---|---|---|
| Stage I | •Any size of tumour •Or presence of regional lymph node spread •No metastasis to distant organs | •Tumour size less than 2 cm •No presence of regional lymph node spread •No metastasis to distant organs |
| Stage II | •Any size of tumour •Or presence of regional lymph node spread •Presence of distant organ metastasis | •Tumour size between 2 and 4 cm • No presence of regional lymph node spread • No metastasis to distant organs |
| Stage III | •Tumour extends beyond the thyroid gland • Or presence of regional lymph node spread | •Tumour extends beyond the thyroid gland •Or presence of regional lymph node spread |
| Stage IV | •Tumour extends to the adjacent trachea or oesophagus •Presence of distant organ metastasis | •Tumour extends to the adjacent trachea or oesophagus •Presence of distant organ metastasis |
Primary Treatment Methods
Surgery serves as the primary treatment for thyroid cancer. Depending on the patient’s condition, the surgeon may perform either a partial or total thyroidectomy. During the procedure, the surgeon examines nearby lymph nodes for cancerous involvement. If cancer has spread beyond the thyroid, adjacent affected tissues will also be removed.
Following complete or near-total thyroid removal, patients require lifelong thyroid hormone replacement therapy to compensate for lost hormonal production. This treatment also helps suppress thyroid-stimulating hormone (TSH) secretion, as elevated TSH levels may stimulate residual cancer cells and potentially cause recurrence.
Postoperative complications may include:
After surgery, if cancer cells remain or have metastasised, patients may require radioactive iodine therapy. This internal radiation treatment involves swallowing radioactive iodine in a capsule or liquid form. Thyroid cancer cells absorb and are destroyed by the radioactive iodine, while normal cells are rarely affected.
Approximately four weeks before treatment, patients must stop taking thyroid hormones as they can interfere with radioactive iodine absorption. Alternatively, recombinant human thyroid-stimulating hormone (TSH) injections may be used to avoid complications from hormone withdrawal. To ensure treatment effectiveness, patients should begin a low-iodine diet two weeks before therapy, avoiding seafood, iodised salt, cough medicines, eggs, cheese, and milk.
For 4-5 days post-treatment, radioactive material is excreted through bodily fluids, requiring hospital isolation until radiation levels drop to safe limits.
Radioactive iodine has no long-term effects, and female patients can later conceive normally, though pregnancy and breastfeeding should be avoided for the first year after treatment.
Radioactive iodine has no long-term effects, and female patients can later conceive normally, though pregnancy and breastfeeding should be avoided for the first year after treatment.
Potential short-term side effects include:
Most side effects are temporary. Patients may consult healthcare professionals to explore potential relief measures if discomfort occurs.
If cancer cells remain in the neck after surgery or if the tumour cannot be completely removed surgically, doctors may consider external beam radiation therapy. This method is more commonly used to treat medullary carcinoma and anaplastic carcinoma. It may also be employed if the cancer recurs.
Before radiation therapy, the hospital will create a custom-fitted transparent plastic mask for the patient’s head and neck. This mask is attached to the treatment table to ensure the patient’s head remains in the correct position during radiation sessions. The entire treatment course typically lasts about six to seven weeks.
Potential side effects of external beam radiation therapy include:
Most side effects are temporary. Patients may consult healthcare professionals to explore potential relief measures if discomfort occurs.
When conventional treatments such as surgery and radioactive iodine become ineffective, targeted therapy drugs may be considered as an alternative treatment option.
Self-Care
After surgery, patients should get out of bed and move around as soon as possible. If bed rest is still required, follow the therapist’s instructions for regular foot movements and deep breathing exercises. To maintain clear airways, patients should rest in a semi-sitting position. Swallowing may be painful after surgery, so a liquid or soft diet may be necessary.
Medication Adherence
Take prescribed medications (such as thyroid hormones, calcium supplements, and vitamin D) as the doctor directs.
Regular Follow-Up Visits
Regular check-ups and follow-up examinations are crucial for detecting cancer recurrence. Even after thyroid removal, there is still a possibility of recurrence. Six months after radioactive iodine treatment, the doctor will arrange a whole-body iodine scan and thyroglobulin blood test to confirm the absence of residual cancer cells. Subsequently, the doctor will perform regular neck examinations and blood tests to monitor for recurrence.
Adequate Nutrition Intake
If treatment side effects temporarily affect normal eating, high-nutrition and high-calorie nutritional supplements can be used as an alternative.
Before radioactive iodine treatment or whole-body radioactive iodine scanning, patients may be required to follow a low-iodine diet as their doctor prescribes. This is because high-iodine foods can interfere with treatment effectiveness.
When following a low-iodine diet, carefully read nutrition labels on food packaging to make appropriate food choices.
*Foods and beverages to avoid:
Categories | Examples |
Seasonings | Iodised salt, sea salt |
Seafood and seafood products | Fish, shellfish, nori, seaweed |
Milk and dairy products | Milk, cheese, yoghurt, butter, cream, ice cream |
Eggs | Egg yolks |
Baked goods | Pizza, bread, cornflakes |
Soy products | Tofu, soy milk, soy sauce, dried bean curd |
Processed and pickled foods | Ham, bacon, sausage, kimchi, pickles, marinated olives |
Products containing artificial red dyes | Syrup, disinfectants, and mouthwash |
Foods containing food colouring E127 | Cola, whiskey, instant coffee or tea |
Others | Dried fruits, nuts, iodine-containing vitamins or supplements |
Foods and beverages are safe to consume
*Sources:
Cancer Online Resource Hub
▣ The information on this website has been reviewed by the HEAL Medical Team and is regularly updated according to the most recent clinical evidence. All content is provided for general informational purposes only and should not replace professional medical advice. Please consult your doctor or another qualified healthcare professional for personalized medical guidance.
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