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HealthInfo Canterbury

Thyroid cancer

Thyroid cancer affects the thyroid gland at the base of your neck. It's usually able to be cured without causing lasting problems.

Thyroid cancer is treated with surgery, which may be followed by radioactive iodine treatment.

The outlook for thyroid cancer is usually very good:

The outlook isn't quite as good for people over 45 or for people who have tumours larger than 4 cm in diameter. Still, even people who can't be cured can live a long time and feel well despite their cancer.

Symptoms of thyroid cancer

The first sign of thyroid cancer is usually a lump (nodule) in your thyroid. But most thyroid lumps aren't caused by a cancer.

Many people don't have any other symptoms. A few people with thyroid cancer complain of pain in their neck, jaw or ear. If the cancer is large enough, it may cause difficulty breathing, choking or shortness of breath if it's pressing on your windpipe. Occasionally, it can cause a hoarse voice if it affects the nerve to your voice box.

Causes of thyroid cancer

We don't know what causes most thyroid cancer. It's more common in people whose thyroid gland has been exposed to radiation, who have a family history of thyroid cancer and who are older than 45. Routine X-rays (such as dental X-rays, chest X-rays and mammograms) don't cause thyroid cancer.

Diagnosing thyroid cancer

Medical professionals can diagnose thyroid cancer by taking a sample of the thyroid nodule (called a fine needle aspirate, or FNA) or removing the nodule during surgery. Thyroid nodules are very common, but less than one in 10 are thyroid cancer.

Types of thyroid cancer

Papillary thyroid cancer is the most common type, making up about 80% of all thyroid cancers. It can happen at any age and tends to grow slowly, spreading first to the lymph glands in your neck. It usually has an excellent outlook (prognosis) even after it has spread to the lymph nodes.

Follicular thyroid cancer makes up about 15% of all thyroid cancers. It tends to happen in slightly older people. Follicular thyroid cancer can grow into the lymph nodes in the neck. It may also grow into blood vessels and then spread to other parts of the body, such as the lungs and bones.

Medullary thyroid cancer accounts for about 5% of all thyroid cancers. It's more likely to run in families and may be associated with other hormone problems. It may also be associated with a faulty gene. In these cases, a blood test can screen family members for the gene defect (called a RET mutation).

Poorly differentiated thyroid cancer is uncommon and is more difficult to treat.

Anaplastic thyroid cancer is the most severe and aggressive form of thyroid cancer and the hardest to treat. Fortunately, it's rare.

Treating thyroid cancer

Surgery is the main treatment for all thyroid cancer.

Usually, the surgeon removes all the thyroid gland, or as much of it as possible. After surgery, you'll need to take thyroid hormones for the rest of your life.

Surgery often cures the thyroid cancer, especially if the tumour is small. If the cancer is large, if it has spread to your lymph nodes, or there's a high risk your cancer will come back, you might also have radioiodine to destroy any thyroid or thyroid cancer cells that are left.

Radioiodine therapy is one reason why papillary and follicular thyroid cancers usually have an excellent outcome. It can seek out and destroy thyroid cancer cells without damaging other tissues in your body.

If your doctor recommends radioiodine therapy, you'll be made hypothyroid (where you have a low level of thyroid hormones) for a short time, because you need high levels of TSH (thyroid stimulating hormone) for it to work. You'll either not start thyroid hormone pills after your thyroid gland is removed or stop your thyroid hormone pills if you are already on the medication. You'll also go on a low-iodine diet for three weeks before the treatment.

Your doctor might prescribe T3 thyroid hormone to take while you're becoming hypothyroid to decrease your symptoms. After you've had the radioiodine, you can start the thyroid pills again.

Radioiodine is safe and has few side effects.

Follow-up

You'll need regular follow-up because thyroid cancer returns in 10 to 20% of patients (sometimes many years after treatment). These follow-up visits will include physical examinations as well as blood tests. You'll have blood tests for your thyroid hormone levels and to measure thyroglobulin, as this can show if the cancer has returned.

Your doctor might also arrange an ultrasound scan of your neck to look for any sign the cancer is returning.

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Written by the Department of Endocrinology, Christchurch Hospital. Adapted by HealthInfo clinical advisers. Last reviewed May 2020.

See also:

Overview of surgery

Radioiodine for thyroid cancer

Radioiodine image courtesy of digitalart at FreeDigitalPhotos.net. Neck examination © Can Stock Photo Inc. / justmeyo.

Page reference: 70792

Review key: HITHC-70792