Thyroid Cancer: Follicular Cancer

This page includes more advanced information on a specific type of thyroid cancer. . . Follicular Thyroid Cancer. Please read our Introduction to Thyroid Cancer page first which gives a general overview of all types of thyroid cancer since it will make this page easier to understand. Papillary, Medullary, and Anaplastic thyroid cancers are covered on separate pages.

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 exists 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 1%). 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.

Editorial Note from Dr. Norman: Virtually all patients with follicular thyroid cancer should be treated with a total thyroidectomy. If your surgeon says that he/she is going to take out all of the thyroid gland on the side of the neck that has the cancer and "some or most" of the thyroid gland on the other side... then find another surgeon. The only reason for a surgeon to not remove the entire thyroid is because they are afraid of injuring the nerve to the voice box... This usually means that they don't do this operation enough. If your surgeon is afraid of doing the complete operation because they may injure something, then think twice about finding another surgeon that does this operation more frequently. Do not let a surgeon remove your thyroid if they don't do this operation very frequently!

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. More detailed information on the different thyroid operations are included on another "Surgical Options" page.

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" with 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.