The thyroid, which lies at the front of the neck, makes hormones that regulate the metabolism. Thyroid cancer is a malignant tumour in this gland. Most lumps that develop here are harmless, but some are cancers that grow and metastasise (invade other parts of the body).
There are different kinds of thyroid tumours
- Papillary and follicular tumours grow slowly, and most are treated successfully. Papillary cancer is the commonest (60–70% of cases).
- Medullary cancer is malignant, but treatable if caught before it spreads beyond the thyroid.
- Anaplastic thyroid cancer is the rarest (1 to 2 percent), and the most dangerous. It spreads and grows fast, and often has a poor outcome.
Thyroid tumour, papillary thyroid cancer, follicular thyroid cancer, medullary thyroid cancer, and anaplastic thyroid cancer.
When DNA is damaged, thyroid cells can grow uncontrollably and form tumours. Various factors encourage this:
- Radiation exposure to the head, neck or chest is a risk factor, such as from high-dose X-rays, which used to be a common medical treatment.
- People who were exposed to radioactive iodine (I-131) in fallout from nuclear explosions, tests or spills are at risk.
- Medullary thyroid cancer can be caused by an inherited mutation.
- Certain inherited illnesses raise the risk of papillary cancer.
- Women are more at risk than men, and women who have children after the age of 30 increase their risk.
- People in specific age groups are more at risk for different kinds of thyroid cancer.
- White and Asian people are more at risk than Africans.
- Lack of iodine in the diet may also increase risk.
A lump in the front of the neck is frequently the first sign of this cancer. Most nodules are benign, but may be cancerous if they are solitary, hard, solid, and grow rapidly. All lumps in the neck should be check on. These growths are usually painless and, apart from the lump in the neck, other symptoms do not appear early in the disease.
Other symptoms of different types of thyroid cancer may include:
- Difficulty breathing
- Difficulty swallowing
- Swollen lymph nodes
- Pain or swelling in the throat or neck
- Hoarseness or altered voice
- Cough, sometimes with bleeding
- Severe diarrhoea
Your doctor will feel your neck for nodules, and ask about your medical history.
Laboratory tests and scans will confirm the diagnosis:
- Blood tests may show abnormal levels of hormones or other chemicals.
- Ultrasound will detect the size, position and texture of nodules.
- Radionuclide scanning detects and analyses nodules.
- Tumour tissue, or a whole excised nodule, can be analysed for cancer cells.
- Genetic tests may show a genetic defect in the RET gene.
Further tests will show if there is any spread (metastasis), and the extent of the spread.
Treatment depends on factors such as the type of tumour, its size and stage, and the patient’s age. It may involve various measures:
- Surgery to remove the whole thyroid (thyroidectomy) is usual. Sometimes, only part of the gland is removed. Nearby lymph nodes may also be removed.
- Radioactive iodine therapy, where a small dose of radioactive iodine 131 taken orally, destroys cancer cells. Medullary and anaplastic cancer do not respond well to I-131 therapy.
- External radiation therapy (radiotherapy) uses high-energy rays to kill cancer cells in the affected areas.
- Hormone treatment is usual for papillary and follicular cancer.
- Chemotherapy drugs can kill cancer cells throughout the body. This only works for some patients.
Further treatment may be necessary if the cancer spreads or recurs. After treatment, patients usually need to take a replacement thyroid hormone tablet daily to replace what your body is not longer producing.
Support groups may be helpful for dealing with emotional aspects of the disease.
When the cancer hasn’t metastasized, surgery is effective.
- Most people (over 95 percent) with papillary cancer are cured.
- Follicular cancer is faster growing and may spread, but over 90 percent of patients are cured.
- 40-50 percent of patients with medullary cancer are cured.
- Anaplastic cancer has the worst prognosis. Average survival after diagnosis is less than 6 months.
The most serious complication of thyroid cancer is metastasis to other tissues.
Various treatments have side effects:
- Surgery may damage nerves, muscles, glands and the voice box.
- Rare side effects of I-131 are male sterility and leukaemia.
- Patients may experience problems from taking too much or too little thyroid hormone.
- External radiation therapy can be exhausting, and irritate the skin.
- Chemotherapy may cause nausea, vomiting, mouth sores and loss of appetite.
When to call your doctor
See your doctor if you feel a lump in your neck or have other symptoms, or think you are at risk of thyroid cancer.
There is currently no preventive treatment.
- If testing shows a defective RET gene, you may choose to have your thyroid removed. Genetic testing will show if family members are at risk.
- Taking potassium iodide protects the thyroid gland during exposure to nuclear radiation.
- A diet high in fruits, vegetables and unsaturated fats generally reduces the risk of cancer.
Reviewed by Dr David Eedes, MB ChB FFRad (T), Clinical oncologist, July 2011