Thyroid cancer

Introduction

In Australia, approximately 3000 people are diagnosed with thyroid cancer each year. The major risk factors include radiation exposure and a solitary thyroid nodule. Only 5 % of thyroid nodules will harbour cancer. Malignancy is more likely to occur in people with a history of thyroid carcinoma. Thyroid carcinoma accounts for approximately 1.5 % of all malignancy and approximately 0.5% of all deaths from cancer. The mortality rate of 6 persons per million population per year coupled with the low incidence suggest favourable prognosis.

Because cancer occurs in approximately 15% of patients with a solitary nodule and clinically silent carcinoma (Under 1 cm) Occur in up to 35% of glands recorded at autopsy or surgery, a selective approach should be used to identify patients when the nodule should be removed. Thyroid carcinoma was documented in 24 cases per million population in 1947, in 39 cases in 1971 and 41 in 1988, the increase from 1947 to 1971 may be secondary to radiation exposure. More than one million people received radiation to the thyroid gland for treatment of benign head and neck diseases such as acne, thymus hyperplasia, keloids and external otitis.

Causes

A risk factor is any factor that is associated with an increased chance of developing a particular health condition, such as thyroid cancer. There are different types of risk factors, some of which can be modified and some that cannot. Having a risk factor does not mean that you will get cancer; not having risk factors doesn’t mean that you will not get cancer. Talk with your doctor if you think you may be at risk.

Although the causes of thyroid cancer are not fully understood, there are a number of factors associated with the risk of developing the disease. These factors include:

• Being female
• Exposure to radiation particularly of the neck. Patients exposed to low doses of therapeutic radiation have a 1 - 7 % chance of developing thyroid cancer with an increasing risk for at least 3 decades after exposure. The highest risk appears to be in children under the age of 7 years. If a patient has a thyroid nodule and a history of irradiation to the thyroid gland a 40% chance exists of having thyroid cancer. 
• Family history of thyroid disease or thyroid cancer
• Certain genetic conditions, such as Familial Medullary Thyroid Cancer (FMTC), Multiple Endocrine Neoplasia type 2A syndrome, and Multiple Endocrine Neoplasia type 2B syndrome
• Patients with other genetic conditions such as Gardener’s syndrome and Cowden’s disease have a higher risk of thyroid malignancy.
• Gardener’s syndrome is associated with multiple polyps in the gastro intestinal tract and colon cancer and carries an increase risk of developing papillary thyroid carcinoma.
• Cowden’s disease is an autosomal dominant condition characterized by a muco-cutaneous lesions and internal malignancy. Patients with Cowden’s disease are prone to the development of breast cancer, colon cancer and malignant thyroid conditions. Cowden’s disease is associated with goitre in 40% of patients and with thyroid carcinoma in 10% of patients. Medullary Carcinoma is often familial, it may occur in association with endocrinopathies.
• Living in iodine deficient area increases the risk of follicular and anaplastic carcinoma. Living in an area of high dietary iodine intake appears to increase the risk of papillary carcinoma. Higher circulating levels of estrogens may minimally increase the risk of thyroid carcinoma.

Other factors that appear to increase the frequency of thyroid carcinoma: 

• Having a history of goitre (enlarged thyroid).
• Residences near volcanoes.
• Possibly alcohol ingestion.
• An enlarging nodule, on thyroid suppressant therapy.
• Development of a nodule in a person of under 14 years of age or over 65 years of age.

If you have any of these risk factors or are concerned about your risk, please see your doctor.

Symptoms

Thyroid nodules (lumps) are common, but are usually not cancer. When a thyroid nodule is found, an ultrasound of the thyroid and a fine-needle aspiration biopsy are often done to check for signs of cancer.

The most common symptoms of thyroid cancer are:

• A lump or swelling in the neck or throat
• Difficulty breathing or shortness of breath
• Difficulty swallowing – this is called dysphagia
• A hoarse voice or a cough that doesn’t go away
• Enlarged lymph nodes in the neck.

There are a number of conditions that may cause these symptoms, not just thyroid cancer. If any of these symptoms are experienced, it is important that they are discussed with a doctor.

Diagnosis & Tests

A number of tests may be performed to investigate symptoms of thyroid cancer and confirm a diagnosis. Some of the more common tests include:

• A physical examination and patient history.
• Examination of a blood sample, Thyroid function tests and tumour markers.
• Imaging of the thyroid, which may include ultrasound, computed tomography (CT) scan or magnetic resonance imaging (MRI).
• Internal examination of the voice box using a laryngoscope – a thin tube with a light on the end of it.
• Taking a sample of tissue (biopsy) from the thyroid gland free hand or under Ultrasound guidance for examination under a microscope.

Types of thyroid cancer and Treatment

Papillary carcinoma

Papillary carcinoma is the most common type of malignancy involving the thyroid gland. It may be multicentric in up to 80% of cases and it frequently involves both lobes. Histologically they can be pure papillary, mixed papillary-follicular and the follicular variant of papillary carcinoma. Mixed papillary-follicular is most common. Minimal (1 cm in diameter) and occult (less than 1.5cm in diameter) are of interest because their incidence exceeds that of papillary carcinoma greater than 1.5 cm and the prognosis is so good, it mandates a more conservative approach than those greater than 1.5cm. The reported incidence of occult varies from 0.45 % to 13 % of Caucasian individuals in Michigan, 28% of Japanese individuals in Japan and 36% of autopsy specimens in Finland. 

Follicular carcinoma 

The less common type, it differs from papillary in several ways. Follicular are more often solitary and many follicular carcinomas are discovered in association with areas of iodine deficiency, while papillary tend to occur in high iodine intake. Follicular carcinoma tends to invade blood vessels and metastasizes to distant sites, most commonly blood, lung and brain. Patients with follicular carcinoma may have distant metastases before the primary tumour becomes evident. The incidence of metastases in follicular is as high as 33%. Cervical lymph node involvement occurs in approximately 10% of cases of follicular carcinoma. Follicular carcinoma is less frequently associated with previous radiation exposure. Finally occult follicular carcinoma is rare.

The rationale for total thyroidectomy is the same. The main difference is that although follicular is solitary it has a higher incidence of distant and metastases especially lung and bone. Total thyroidectomy facilitates radioiodine ablation of any distant metastases. 

After surgery patients are treated with sufficient thyroid hormone to suppress TSH (Thyroid Stimulating Hormone) production and lower the recurrence rates. Monitoring serum thyroglobulin levels is a sensitive and specific method of detecting recurrent disease. Since thyroglobulin is only produced by thyroid tissue it follows that total thyroidectomy should result in undetectable thyroglobulin levels. In extensive studies no metastases were found in patients in whom thyroglobulin levels were undetectable. 

Certain factors have a profound influence on prognosis of papillary thyroid carcinoma. Age at the time of diagnosis is perhaps the most important. There is a consistent, direct correlation between age and mortality, which increases progressively from children to those over the age of 60. In addition, the size of the tumour has an impact on survival. When the tumour is greater than 1.5cm or invades the thyroid capsule, recurrence is more frequent and deaths occur more often. The presence of lymph nodes in patients under the age of 40 has little effect on mortality. In patients over 40 with lymph node metastases the mortality is greater. 

Follicular carcinoma that show vascular invasion is the most aggressive carcinoma, a 20-year mortality rate of 84% has been reported compared with 2.8 % in patients with equivocal invasions. Increasing age and the presence with distant metastases is associated with poor prognosis. The size of the tumour and the presence of lymph node metastases do not have important prognostic implications.

Mortality appears to be greater in patients with follicular carcinoma rather than those with papillary carcinoma. Of patients dying of follicular carcinoma approximately 75% succumb to distant metastases and the remainder to locally invasive disease.

Rationale for total Thyroidectomy

• Recurrence is lower in patients who have undergone total thyroidectomy. Recurrent cancer develops in the remaining contralateral lobe in 7% of patients and 1.5 of these patients die of thyroid cancer.
• Eliminates the 1% risk of a differentiated thyroid cancer changing to an undifferentiated cancer. 
• Total thyroidectomy eliminates the microscopic foci of cancer present in up to 85% of patients.
• Thyroglobulin is a more sensitive marker of recurrence when all normal thyroid tissue is removed.
• Radioactive Iodine can be used to detect and treat local or distant metastases.

Surgical technique

During surgery to the thyroid gland an incision is made in the front of the neck along the collar line, just under the Adam’s apple. The surgeon removes part or the entire thyroid gland taking care to avoid injury to adjacent blood vessels and nerves. Every attempt is made to preserve the parathyroid glands, as they produce PTH (parathyroid hormone) which controls levels of Calcium in the blood). The incision is closed with metal clips or sutures. A drain tube attached to a plastic bottle rarely used in selected cases to prevent fluid accumulation. The drain tube is usually removed one or two days after surgery. The skin closures either dissolve or are removed a few days following surgery.

As you recover from the anaesthetic, you will be sleepy for the first few hours. You will be raised in a sitting position with your neck well supported. This position will help reduce the swelling. Your breathing, pulse, blood pressure, temperature and incision will be monitored regularly. You will also be assessed for signs of low calcium. By the day following surgery, you will be able to sit in a chair and walk short distances. Patients usually stay in hospital for one or two days. Pain relieving medicine will be prescribed. An intravenous line will be providing fluid until you are ready to drink. Swallowing and eating may be difficult for the first day or two.

Tell your doctor if you have any of the following:

• Breathing difficulty.
• Muscle spasms.
• Twitching or tingling in your lips or at your fingertips.
• Dressing soaked in blood.

Most recover fairly quickly after surgery and you should be able to resume most normal activities after one or two weeks. Recovery from thyroid surgery is usually uncomplicated, but the following problems may occur:

• Difficulty in breathing
• Bleeding
• Injury to the laryngeal nerve, and this can cause hoarseness. This nerve controls the vocal box. Of every hundred patients one or two will have injury to the laryngeal nerve. Patients with cancer or very large goitre or previous surgery are more at risk of nerve injury.
• Damage to the parathyroid glands. Calcium supplements may be needed if calcium levels are low. Of every hundred patients who have total thyroidectomy two will need to take calcium supplements for life due to permanent loss of parathyroid function.
• "Thyroid Storm". This is rare, and occurs when too much thyroid hormone is released into the patient’s blood stream during surgery.
• If you have had total thyroidectomy you will need to take thyroid hormone replacement medication for the rest of your life.
• If all the parathyroid glands have been removed, calcium supplements and other medicines may be needed to maintain calcium levels.

General risks of Surgery

• Heart and Circulation Problems, such as heart attacks and clot formation.
• Wound infections.
• Keloid Scar (overgrowth of scar tissue).

This is intended to provide you with information. It is not a substitute for advice from your surgeon, and does not contain all known facts about the treatment of thyroid gland disorders.

Visit Cancer Australia to read about Thyroid Cancer Treatment.