How common is it?

In most areas of the world, the incidence of thyroid cancer has increased over the last few decades, but related mortality has been declining.¹ Incidence rates in high-income countries are double those in low- and middle-income countries.¹

In Singapore, thyroid cancer is the eighth most common cancer in women, with an annual incidence of 1100 cases per year. It is more common in women, with a higher incidence in Chinese and Malays compared with Indians. It is also diagnosed more commonly in the younger age group compared to other cancers, with most cases occurring in patients below age 60 years.²

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Who is at risk ?

• Women – thyroid cancer affects more women than men^{3
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• A family history of thyroid cancer^{4
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• Exposure to high levels of radiation to the head and neck region (e.g., radiation therapy)^{4
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• Certain inherited genetic conditions that increase risk of thyroid cancer, such as familial medullary thyroid cancer, multiple endocrine neoplasia, Cowden’s syndrome and familial adenomatous polyposis⁴

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How is thyroid cancer diagnosed?

Thyroid cancer may present as a thyroid nodule without causing symptoms. Nodules are often detected incidentally, for example by CT or ultrasound scans performed for other reasons.

An ultrasound scan will be performed to determine the size and features of the nodule. An ultrasound guided fine needle aspiration biopsy of the nodule may be performed if there are suspicious ultrasound features. The biopsy takes cell samples from the nodule which is examined by microscopy to determine if there are cancers cells. Fortunately, less than one in 10 nodules are cancerous.⁵ 

The diagnosis of thyroid cancer may come as a shock and is usually followed by a flood of emotions such as sadness, fear, anger and helplessness. Learning more about your illness and the medical care available may help you overcome your fear and any feelings of helplessness. It will also allow you to take an active part in the treatment process. The good news is that thyroid cancer can be treated and often cured.

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Types of thyroid cancers

Thyroid cancers are classified based on the types of cells found in the tumour.

Papillary and follicular thyroid cancers are known as well-differentiated thyroid cancers:⁵

• Papillary thyroid cancer (PTC) is the most common type of thyroid cancer, accounting for up to 80% of all thyroid cancers. PTC can occur at any age. This type of thyroid cancer grows slowly and may spread to the lymph nodes in the neck. PTC generally responds well to treatment and is highly curable.
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• Follicular thyroid cancer (FTC) accounts for up to 15% of all thyroid cancers. FTC can spread through blood to the bones and other organs such as lungs. Cancers that spread beyond the thyroid gland may be more challenging to treat.

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Other types of thyroid cancers:⁵

• Medullary thyroid cancer (MTC) accounts for about 2% of all thyroid cancers. Approximately a quarter of people with this type of thyroid cancer have a family history of the disease as a result of a genetic mutation.
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• Anaplastic thyroid cancer (ATC) is the most aggressive type of thyroid cancer and the most difficult to treat. It can grow quickly and often spread to other parts of the body early. This type of cancer is rare and accounts for less than 2% of all thyroid cancers.

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Treatment of thyroid cancer

The primary treatment for all forms of thyroid cancer is the removal of part of or the entire thyroid gland by surgery. If the tumor has already spread into the lymph nodes in the neck or upper chest, then these lymph nodes will also be removed. After surgery, you will be prescribed appropriate medication. You will have to take thyroid hormone medication on a permanent basis if the entire thyroid gland has been removed.⁵ 

If your tumour is large or has spread to other tissues, you will probably be recommended to undergo radioactive iodine (RAI) therapy after thyroid surgery. RAI will kill the remaining cancer cells, even those in distant tissues. In preparation for this treatment, you will be made hypothyroid either by stopping thyroid hormone medication or injecting synthetic thyroid stimulating hormone (TSH). This is to ensure optimal uptake of the RAI by the thyroid cancer cells. You will also need to go on a low-iodine diet. The less iodine in your body, the more effective the treatment.⁵ You should speak to your doctor about how to balance the potential risks against the benefits of RAI.

In patients with advanced stages of thyroid cancer, surgery and RAI treatment may not work. Your doctor will then propose radiation therapy, chemotherapy, or a combination of both.⁵

After successful treatment, periodic follow-up examinations are necessary to be sure that the cancer has not come back. Apart from physical examination, these check-ups may include ultrasound scans of the neck area and blood tests to check if the cancer recurs.⁵ 

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Summary

• Thyroid cancer may present as a thyroid nodule without causing symptoms
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• An ultrasound scan and thyroid biopsy are required to make the diagnosis of thyroid cancer
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• Papillary thyroid cancer, the most common form of thyroid cancer is usually slow growing and highly curable

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