Educational Material - Health Guides on Thyroid Disease

Thyroid Cancer

Thyroid cancer is not very common but it is common enough so that patients should be aware of that possibility, particularly for those who have a nodule (i.e. a localized swelling) in the thyroid gland (see Health Guide #4 - Thyroid Nodules). It is estimated that 4500 new cases will be diagnosed in 2009 in Canada. Thyroid nodules are more common in females than males; however, males have a greater risk than females for cancer occurring in a thyroid nodule.

Types of Thyroid Cancer
There are different types of thyroid cancer but the most common, occurring in 80% of cases, is known as Differentiated Thyroid Cancer (papillary, follicular or mixed papillary and follicular forms). Provided a careful history is obtained, 5-10% of patients with Differentiated Thyroid Cancer will have a positive family history. Anaplastic Thyroid Cancer is a rare type of cancer with a poor prognosis. Occasionally individuals develop lymphoma of the thyroid gland or with metastasis from other cancer types. Medullary Thyroid Cancer is a rare tumor, arising not from the follicular cells that produce the thyroid hormone but from C-cells which are also present in the thyroid.

In approximately 25% of cases there may be involvement of other endocrine glands such as the adrenal, and parathyroid glands. Problems with intestinal motility or special physical features (long arm span, neurinomas, or small bumps, on the lips and tongue) may also be evident. This combination of features is known as multiple endocrine neoplasia syndrome and is a hereditary condition for which the gene is known. It is currently recommended that all patients with medullary thyroid cancer benefit from genetic counselling and/or genetic screening that is offered in specialized centres across Canada. Patients with medullary cancer should ensure that family members are aware of the genetic screening that is predictive of future disease development. Genetic screening is more sensitive than traditional biochemical tests and examinations. If an individual has the genetic mutation leading to multiple endocrine neoplasia and medullary thyroid cancer there is a 50% chance of passing it onto their children.

Radiation Exposure
Previous exposure to head and neck irradiation in childhood, adolescence or even adulthood has been recognized as an important contributing factor for the development of differentiated thyroid cancer. Years ago, patients received x-ray treatments for acne, skin problems of the face, tuberculosis in the neck, fungus diseases of the scalp, blood vessel tumors of the face, enlarged thymus, tonsillitis, sore throats, chronic coughs, and even excess facial hair. This therapy is NO longer performed. It became recognized that the thyroid gland is particularly sensitive to the effects of radiation resulting in thyroid tumors with a 30% risk for cancer. In addition, patients who require radiation for the treatment of certain types of cancer in or near the head and neck area may also have an increased risk for the development of thyroid nodules and thyroid cancer. If you have had radiation for any such problems, consultation with your physician would be appropriate to ensure your thyroid gland is functioning normally and does not have any nodules.

In contrast to other cancers, differentiated thyroid cancer is almost always curable. To confirm whether a thyroid nodule is present, ultrasound imaging procedures are used. However, a Fine Feedle Aspiration Biopsy is the BEST diagnostic measurement by far to detect which nodules will require surgical intervention due to suspicion of cancer and exclude those which do not.

The most effective form of initial thyroid cancer therapy is surgery (see Health Guide #11 - Surgical Treatment of Thyroid Disease). Because of the excellent outlook for most thyroid cancers, some surgeons feel that it is sufficient to remove only a portion of the gland. However, there is a growing body of evidence based upon long term follow-up which indicates it is worthwhile to safely remove as much of the thyroid gland as possible. This more aggressive approach will avoid recurrences and optimize subsequent non-surgical measures such as radioactive iodine therapy. Although a total thyroidectomy slightly increases the risk for possible deficiency in calcium by the inadvertent removal of nearby parathyroid glands, this risk should be minimized when the thyroid cancer surgery is performed by an experienced surgeon. The potential for vocal cord damage is also extremely rare in experienced hands.

In about 30% of patients, the cancer may spread from the thyroid gland to lymph glands nearby in the neck. If this occurs, the lymph glands should be removed by an operation called a neck dissection. The extent of the removal depends in part on how many lymph nodes appear affected by the cancer. Usually this can be achieved through cosmetically satisfactory incisions. Occasionally, the incision may have to be elongated. Apart from some transient swelling of the face, the removal of such lymph glands results in NO serious bodily deprivation or dysfunction.

Radioactive Iodine Therapy
Depending on the findings at the time of surgery, radioactive iodine may be considered post-operatively. Radioactive iodine was traditionally administered in either a capsule or liquid form usually 4-6 weeks after completing the necessary surgery. In order for the radioactive iodine to work, thyroid replacement (tablets) are withheld during this time. Unfortunately, the patient must endure the consequences of an underactive thyroid which may include fatigue, muscle cramps, puffiness and constipation. However, knowing it is absolutely necessary and that thyroid replacement will begin at the completion of treatment helps patients deal with this consequence. Health Canada has recently approved the use of recombinant TSH (Thyrogen®) for the treatment of thyroid remnant ablation. Thus, for most patients it will be possible to avoid the withdrawal of thyroid replacement therapy and the unpleasant symptoms of hypothyroidism.

Radioactive iodine therapy is simple but depending upon dosage and local facilities may require isolation in a hospital room for several days. Although transient neck discomfort, decreased saliva formation and alteration in taste may rarely occur, there are usually no significant side effects. Occasionally this treatment is repeated if residual or recurrent thyroid cancer is detected. Recent data suggests a slight increase in secondary cancers in patients receiving high cumulative doses of radioiodine. Management by an experienced multidisciplinary team could help determine the appropriate treatment for each thyroid patient.

External Radiation Therapy
X-ray radiation from an external source by "cobalt beam" is rarely necessary but could be recommended when the thyroid cancer cannot be completely removed to improve local control of the disease. External radiation is administered over a 4 to 6 week interval in small divided doses to the neck region. This may induce a secondary skin reaction due to the formation of small blood vessels and pigment darkening of the skin. However, this does not invariably occur.

Traditional chemotherapy is not very effective against thyroid cancer and is thus seldom used. Encouraging results have been obtained in the past years using new molecules known as tyrosine kinase inhibitors and anti0angiogenic factors. These drugs interfere with the vascular supply along with various enzymes and proteins, which are responsible for the growth and division of the cancer cells. They also have the advantage of having a relatively limited and milder spectrum of side effects.

Post Treatment Check-ups
Following surgery and radioactive iodine therapy, thyroid hormone pills are prescribed. Thyroid hormone not only ensures proper metabolism but suppresses the pituitary hormone, thyrotropin (TSH) which can stimulate thyroid cancers to grow. Unlike patients with an underactive thyroid, thyroid cancer patients are treated with dosages sufficient to maintain the serum TSH level below normal to prevent further growth of the cancer. This requires thyroxine (Euthyrox®, Synthroid®) doses higher than the ones used for hypothyroidism. The average dose of Syntrhodi in cancer patients is approximately 2-2.5 micrograms/kg of body weight. The level of thyroid function is checked periodically by both clinical examination and laboratory tests. Thyroid cancer patients are examined at regular 6 to 12 month intervals to ensure that there is no evidence of recurrent cancer. The frequency of follow-up procedures is decreased as time passes but should be maintainted long term.

Measurement of serum thyroglobulin (the precursor of thyroid hormone) is the single best test to determine whether recurrences have occurred especially when combined with neck ultrasounds. The sensitivity of the serum thyroglobulin measurement can be increased by previous administration of recombinant TSH (Thyrogen®). Other imaging modalities such as computed tomography(CT scan) of the chest or PET scan can also be used to identify residual disease.

For the most common forms of papillary and papillary-follicular thyroid cancer, the 5 and 10 year survival rates are IN EXCESS OF 95%. The risk for recurrence is higher in patients over the age of 45 or if the thyroid cancer has extended outside of the thyroid gland at the time of the original diagnosis. However, early detection and treatment often averts such consequences.

Patients usually have questions regarding thyroid cancer. Here are some of them. If you have a different question, you might write to the Thyroid Foundation of Canada and answers may be published in the Thyrobulletin by a consultant doctor.

Questions and Answers

  1. Q: Does smoking or drinking cause thyroid cancer?

    A: Smoking and drinking are not related to thyroid cancer. Such habits of course are better avoided for overall good health but they neither cause nor aggravate the course of thyroid gland malignancy.

  2. Q: Does thyroid cancer spread throughout the body and how can you tell if this is so?

    A: Thyroid cancer rarely spreads throughout the body. Most thyroid cancers are cured by the initial operation. Although thyroid cancer may extend to lymph glands in the neck, the removal of these lymph glands is usually quite feasible and curative. Infrequently cancers do spread to lung and bone and can be detected by x-ray and scanning imaging procedures. Such a situation requires treatment by radioactive iodine or other x-ray therapy procedures and occasionally surgical removal. For the rare but more aggressive types of cancer, treatment with chemotherapy and x-ray therapy may be recommended.

  3. Q: How likely are my chances of dying of thyroid cancer even with all this treatment?

    A: Other than skin cancer, the most common types of thyroid cancer have the best longterm outcome when promptly treated compared to all other types of cancer. The majority of patients are totally cured by treatment.

  4. Q: How is thyroid cancer detected?

    A: Thyroid cancer is frequently detected by the patient becoming aware of a lump in the neck. Half such cases are detected by a physician during a routine physical examination for an unrelated problem. Thyroid cancer does not cause pain and rarely produces symptoms. Virtually all patients with thyroid cancer have normal metabolism and thyroid tests.

  5. Q: What are the side effects of treatment? Will I lose my voice or have a large scar?

    A: The usual treatment of thyroid cancer involves the removal of at least a portion or all of the thyroid gland through a small neck incision. It is infrequent for patients to have any problem with a voice disorder or calcium imbalance as a consequence of the surgery. The removal of lymph glands may require a larger incision, but this is usually low in the neck and is still compatible with a good cosmetic result. In some cases where voice problems persist after surgery, referral and treatment by a voice therapist usually improves the situation.

  6. Q: What can I do to ensure that I have the very best result of treatment for my thyroid cancer?

    A: It is important that nodules in the thyroid gland or in the neck area be appropriately diagnosed at an early stage. You should see your family doctor who will assess the situation and most likely refer you to the appropriate specialist to confirm the diagnosis and administer the correct treatment. Early detection and treatment almost always results in a complete eradication and cure!

  7. Q: Will I have to stop my thyroid tablets if radioactive iodine is being given?

    A: Yes, for 3 to 6 weeks. The only way the radioactive iodine can "get into" the thyroid and work is if your TSH level becomes elevated. This will occur when you stop your thyroid hormone. Unfortunately, during this time you will likely experience the effects of an underactive thyroid which may include fatigue, muscle cramps, puffiness and constipation. In selected patients, considered low risk, that receive radioiodine for thyroid remnant ablation, recombinant human TSH (Thyrogen®) can be used instead of thyroid tablet withdrawal.

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