There are over 11,000 new cases of thyroid cancer each year in the United States. Females are more likely to have thyroid cancer at a ratio of three to one. Thyroid cancer can occur in any age group, although it is most common after age 30 and its aggressiveness increases significantly in older patients. The majority of patients present with a nodule on their thyroid which typically does not cause symptoms.
Occasionally, symptoms such as hoarseness, neck pain, and enlarged lymph nodes do occur. Although as much as 10 % of the population will have thyroid nodules, the vast majority are benign. Only approximately 5% of all thyroid nodules are malignant. A nodule which is cold on scan (shown in photo outlined in red and yellow) is more likely to be malignant, nevertheless, the majority of these are benign as well.
Types of Thyroid Cancer
There are four types of thyroid cancer some of which are much more common than others.
Thyroid Cancer Type and Incidence
Papillary and mixed papillary/follicular ~ 75%
Follicular and Hurthle cell ~ 15%
Medullary ~ 7%
Anaplastic ~ 3%
What’s the Prognosis ??
Most thyroid cancers are very curable. In fact, the most common types of thyroid cancer (papillary and follicular) are the most curable. In younger patients, both papillary and follicular cancers can be expected to have better than 95% cure rate if treated appropriately. Both papillary and follicular cancers are typically treated with complete removal of the lobe of the thyroid which harbors the cancer, PLUS, removal of most or all of the other side.
Medullary cancer of the thyroid is significantly less common, but has a worse prognosis. Medullary cancers tend to spread to large numbers of lymph nodes very early on, and therefore requires a much more aggressive operation than does the more localized cancers such as papillary and follicular. This cancer requires complete thyroid removal PLUS a dissection to remove the lymph nodes of the front and sides of the neck.
The least common type of thyroid cancer is anaplastic which has a very poor prognosis…it tends to be found after it has spread and is not cured in most cases. Often an operation cannot remove all the tumor.
What About Chemotherapy ??
Thyroid cancer is unique among cancers, in fact, thyroid cells are unique among all cells of the human body. They are the only cells which have the ability to absorb Iodine. Iodine is required for thyroid cells to produce thyroid hormone, so they absorb it out of the bloodstream and concentrate it inside the cell. Most thyroid cancer cells retain this ability to absorb and concentrate iodine. This provides a perfect “chemotherapy” strategy. Radioactive Iodine is given to the patient and the remaining thyroid cells (and any thyroid cancer cells retaining this ability) will absorb and concentrate it. Since all other cells of our bodies cannot absorb the toxic iodine, they are unharmed. The thyroid cancer cells, however, will concentrate the poison within themselves and the radioactivity destroys the cell from within. No sickness. No hair loss. No nausea. No diarrhea. No pain. More about this on the pages for each specific thyroid cancer type.
Not all patients with thyroid cancer need radioactive iodine treatments after their surgery. This is important to know. Others, however, should have it if a cure is to be expected. Just who needs it and who doesn’t is a bit more detailed than can be outlined here. Patients with medullary cancer of they thyroid usually do not need iodine therapy…because medullary cancers almost never absorb the radioactive iodine. Some small papillary cancers treated with a total thyroidectomy may not need iodine therapy as well, but for a different reason. These cancers are often cured with simple (complete) surgical therapy alone. Important!!! This varies from patient to patient and from cancer to cancer. Don’t look for easy answers here. This decision will be made between the surgeon, the patient, and the referring endocrinologist or internist.Remember, radioactive iodine therapy is extremely safe. If you need it, take it.
Follicular carcinomas are the second most common thyroid cancers (~15 %). Follicular carcinoma is considered more malignant (aggressive) than papillary carcinoma. It occurs in a slightly older age group than papillary and is also less common in children. In contrast to papillary cancer, it occurs only rarely after radiation therapy. Mortality is related to the degree of vascular invasion. Age is a very important factor in terms of prognosis. Patients over 40 have a more aggressive disease and typically the tumor does not concentrate iodine as well as in younger patients. Vascular invasion is characteristic for follicular carcinoma and therefore distant metastasis is more common. Distant metastasis may occur in a small primary. Lung, bone, brain, liver, bladder, and skin are potential sites of distant spread. Lymph node involvement is far less common than in papillary carcinoma (8-13%).
Characteristics of Follicular Thyroid Cancer
Peak onset ages 40 through 60
Females more common than males by 3 to 1 ratio
Prognosis directly related to tumor size [less than 1.0 cm (3/8 inch) good prognosis]
Rarely associated with radiation exposure
Spread to lymph nodes is uncommon (~10%)
Invasion into vascular structures (veins and arteries) within the thyroid gland is common
Distant spread (to lungs or bones) is uncommon, but more common than with papillary cancer
Overall cure rate high (near 95% for small lesions in young patients), decreases with advanced age
Management of Follicular Thyroid Cancer
Considerable controversy exits when discussing the management of well differentiated thyroid carcinomas (papillary and even follicular). Some experts contend than if these tumors are small and not invading other tissues (the usual case) then simply removing the lobe of the thyroid which harbors the tumor (and the small central portion called the isthmus) will provide as good a chance of cure as removing the entire thyroid. These proponents of conservative surgical therapy relate the low rate of clinical tumor recurrence (5-20%) despite the fact that small amounts of tumor cells can be found in up to 88% of the opposite lobe thyroid tissues. They also site some studies showing an increased risk of hypoparathyroidism and recurrent laryngeal nerve injury in patients undergoing total thyroidectomy (since there is an operation on both sides of the neck). Proponents of total thyroidectomy (more aggressive surgery) site several large studies that show that in experienced hands the incidence of recurrent nerve injury and permanent hypoparathyroidism are quite low (about 2%). More importantly, these studies show that patients with total thyroidectomy followed by radioiodine therapy and thyroid suppression, have a significantly lower recurrence rate and lower mortality when tumors are greater than 1.0 cm. One must remember that it is also desirable to reduce the amount of normal gland tissue that will take up radioiodine.
It also must be kept in mind that frozen section (the rapid way that the tumor is examined under the microscope for characteristics of cancer) may be unreliable in making definitive diagnosis of follicular cancer at the time of surgery. This problem is not seen with other types of thyroid cancer.
Based on the these studies and the above natural history and epidemiology of follicular carcinoma, the following is a typical plan: Follicular carcinomas that are well circumscribed, isolated, minimally invasive, and less than 1cm in a young patient (< 40) may be treated with hemithyroidectomy and isthmusthectomy. All others should probably be treated with total thyroidectomy and removal of any enlarged lymph nodes in the central or lateral neck areas.
The Use of Radioactive Iodine Post-Operatively
Thyroid cells are unique in that they have the cellular mechanism to absorb iodine. The iodine is used by thyroid cells to make thyroid hormone. No other cell in the body can absorb or concentrate iodine. Physicians can take advantage of this fact and give radioactive iodine to patients with thyroid cancer. There are several types of radioactive iodine, with one type being toxic to cells. Follicular cancer cells absorb iodine (although to a lesser degree in older patients) and therefore they can be targeted for death by giving the toxic isotope (I-131). Once again, not everybody with follicular thyroid cancer needs this therapy, but those with larger tumors, spread to lymph nodes or other areas, tumors which appear aggressive microscopically, tumors which invade blood vessels within the thyroid, and older patients may benefit from this therapy. This is extremely individualized and no recommendations are being made here or elsewhere on this web site…too many variables are involved. But, this is an extremely effective type of “chemotherapy” will few potential down-sides (no hair loss, nausea, weight loss, etc.).
Uptake is enhanced by high TSH levels; thus patients should be off of thyroid replacement and on a low iodine diet for at least one to two weeks prior to therapy. It is usually given 6 weeks post surgery (this is variable) can be repeated every 6 months if necessary (within certain dose limits).
What About Thyroid Hormone Pills After Thyroid Cancer Surgery?
Regardless of whether a patient has just one thyroid lobe and the isthmus removed, or the entire thyroid gland removed, most experts agree they should be placed on thyroid hormone for the rest of their lives. This is to replace the hormone in those who have no thyroid left, and to suppress further growth of the gland in those with some tissue left in the neck. There is good evidence that follicular carcinoma (like papillary cancer) responds to thyroid stimulating hormone (TSH) secreted by the pituitary, therefore, exogenous thyroid hormone is given which results in decreased TSH levels and a lower impetus for any remaining cancer cells to grow. Recurrence and mortality rates have been shown to be lower in patients receiving suppression.
What Kind of Long-Term Follow Up is Necessary?
In addition to the usual cancer follow up, patients should receive a yearly chest x-ray as well as thyroglobulin levels. Thyroglobulin is not useful as a screen for initial diagnosis of thyroid cancer but is quite useful in follow up of well differentiated carcinoma (if a total thyroidectomy has been performed). A high serum thyroglobulin level that had previously been low following total thyroidectomy especially if gradually increased with TSH stimulation is virtually indicative of recurrence. A value of greater than 10 ng/ml is often associated with recurrence even if an iodine scan is negative.
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