Thyroid cancer occurs in the cells of the thyroid, which is a butterfly-shaped gland located at the base on the neck. The thyroid produces hormones that regulate the heart rate, body temperature and weight.

There are many types of thyroid cancer. Some grow very slowly and others can be very aggressive. Most thyroid cancer cases can be cured with treatment.

Types of thyroid cancers

Papillary thyroid cancer

This is the most common kind of thyroid cancer, accounting for about 75% of cases. Papillary thyroid cancers are usually slow growing, but they tend to spread to the lymph nodes in the neck. Most of these cancers can be treated successfully.

There are many subtypes of papillary thyroid cancer. Some less common subtypes of this cancer (follicular variant, tall cell, insular, diffuse sclerosing) tend to be more aggressive and may grow and spread more quickly.

Follicular thyroid cancer

Follicular thyroid cancer is the second most common type of thyroid cancer which accounts for about 15% of cases. This cancer type tends to spread via the bloodstream to other parts of the body such as the lungs and bones.

Medullary thyroid cancer

Medullary thyroid cancer is much less common, accounting for about 5% of thyroid cancers. These cancers arise from the parafollicular C cells in the thyroid. These cells are usually responsible for producing a hormone called calcitonin, which helps to control the level of calcium in the body. Although the outcome of treatment for medullary thyroid cancer is not as good as for papillary and follicular thyroid cancers, many patients can still be treated successfully.

Anaplastic thyroid cancers

Anaplastic thyroid cancer is the most rare and accounts for about 2% of thyroid cancers. These cancers tend to be very aggressive and grow very quickly and spread rapidly to other parts of the body.

Thyroid cancer incidence in Singapore

Thyroid cancer is more common in women than men. In Singapore, it is the 8th most common cancer diagnosed in women. Thyroid cancer is commonly diagnosed at a younger age than most other cancers, with most cases occurring in patients below the age of 60 years.

Thyroid cancer typically does not cause any signs or symptoms early in the disease. As thyroid cancer grows, it may cause:

• A painless lump on the front of the neck, just next to the voice box/windpipe
• Voice changes, such as increasing hoarseness when speaking
• Difficulty swallowing
• Pain in the neck and throat
• Swollen glands in the neck (enlarged lymph nodes on the side of the neck)

When to see a doctor

Make an appointment with your doctor if you experience any signs or symptoms that worry you.

There is no known way to prevent thyroid cancer, but the following factors may reduce risk:

• Avoid unnecessary exposure to radiation around the neck area, including radiation from medical imaging procedures, especially in young children.
• Those with inherited genetic conditions that increase the risk of medullary thyroid cancer may wish to discuss the risk with a genetic counsellor.

It is not clear what causes thyroid cancer, but factors that may increase the risk of thyroid cancers include:

• Being female – thyroid cancer affects more women than men
• A family history of thyroid cancer
• Exposure to high levels of radiation – e.g. radiation therapy
• Certain inherited genetic conditions such as familial medullary thyroid cancer, multiple endocrine neoplasia, Cowden’s syndrome and familial adenomatous polyposis

Tests and procedures used to diagnose thyroid cancer include:

• Physical examination
  The doctor will examine the neck to feel for physical changes in the thyroid, such as thyroid nodules. The doctor will also ask you about possible risk factors such as past exposure to radiation and if you have a family history of thyroid tumours.


• Blood test for thyroid function
  A blood test may be done to measure the levels of the thyroid hormones and thyroid-stimulating hormone (TSH) and check if the thyroid is functioning normally.


• Fine-needle Aspiration Cytology (FNAC)
  If a lump in the neck is detected, the doctor may recommend a biopsy to evaluate the lump. FNAC biopsy is a procedure where the doctor passes a small needle through the lump to remove a sample of cells for further testing. These cells will be examined in the lab under a microscope to look for signs of cancer.


• Ultrasound scan
  An ultrasound scan uses sound waves to produce an image of the thyroid and neck structures on a screen. This scan is very useful for evaluating thyroid nodules and look for features that may indicate that the thyroid nodule is cancerous. It is also useful for looking for any enlarged lymph nodes in the neck. The ultrasound scan is painless and there is no ionising radiation involved.


• Computer Tomographic (CT) scan
  The CT scan uses ionising radiation to produce an image and may involve the use of a contrast dye which is injected through a vein to make the details of the scan easier to interpret. This scan helps the doctor determine whether the cancer has spread beyond the thyroid.

Treatment for thyroid cancer depends on several factors, such as staging of the cancer, other existing health conditions the patients may have and their personal preferences.

Thyroid cancer is usually treated with surgical removal of the thyroid. Some patients may require more than one type of treatment, such as surgery in combination with chemotherapy or radiation therapy.

Surgery for thyroid cancer

This is the preferred primary treatment option for patients who are fit for surgery.

• Thyroidectomy (removing all or most of the thyroid)
  Doctors usually recommend removing the entire thyroid to treat the thyroid cancer. This is done via an incision at the front of the neck. In suitable cases, the thyroid may be removed via an advanced robotic approach, with the scar hidden behind the ear or the armpit.
  
• Thyroid lobectomy (removing a portion of the thyroid)
  Doctors may opt to remove only one side (lobe) of the thyroid if the cancer is very small. This is usually recommended if it is a slow-growing thyroid cancer in one part of the thyroid and no suspicious nodules are found in other areas of the thyroid.
  
• Removing lymph nodes in the neck
  When removing the thyroid, the doctor may also remove nearby lymph nodes in the neck.

Radioactive iodine treatment for thyroid cancer

Radioactive iodine treatment is often used after surgery to eliminate any remaining cancerous thyroid cells and target secondary tumour sites (in the event the cancer has spread to other parts of the body). This treatment may also be used to treat thyroid cancer that recurs after treatment.

Radioactive iodine is usually administered orally, either in a capsule or liquid form. It is primarily taken up by the thyroid cells and cancer cells, reducing the risk of harming healthy cells. The radioactionpatient will pass most of the radioactive iodine out in their urine within a few days, but the treatment will continue to be effective between one to three months.

Radiation therapy/ Radiotherapy for thyroid cancer

Radiation therapy uses targeted rays to kill cancer cells. This treatment option is used in cases where surgery cannot be performed or radioactive iodine treatment has been ineffective. It can also be used to slow the growth of cancer that has spread to the bones.

Thyroid hormone (thyroxine) therapy

After surgery to remove the thyroid, patients will need to take thyroid hormone medication for life. This is usually an oral medication that is taken once daily. This medication serves a dual purpose – it replaces thyroxine which would have been produced by the thyroid and it helps to significantly reduce the growth of cancer cells by suppressing the hormones that stimulate the thyroid.

Targeted therapy
Targeted therapy uses drugs that attack specific features of the thyroid cancer, for e.g., certain genetic mutations or the blood vessels that supply the cancer, in order to stop the growth and spread of the cancer cells. These treatments are offered when the thyroid cancer has spread to other parts of the body and are no longer responding to radioactive iodine treatment.

After surgery, you will be given regular outpatient appointments to see your team of doctors. During these appointments, you may have blood tests and scans to check if the cancer recurs.

It is important to follow your doctor's advice, keep to your clinic visits and do the recommended scans and tests, so that timely treatment can be administered if the cancer recurs or other problems occur.