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Follicular Thyroid Cancer

Follicular thyroid cancer is the second most common type of thyroid cancer, making up about 10 to up to 15% of all thyroid cancers. Follicular carcinoma (also called Follicular thyroid cancer) is called a “well differentiated” thyroid cancer like papillary thyroid cancer, but it is typically a bit more malignant (aggressive) than papillary cancer. Follicular thyroid cancer occurs in a slightly older age group than papillary thyroid cancer does and is also less common in children. In contrast to papillary thyroid cancer, follicular thyroid cancer occurs only rarely after radiation exposure. Death from follicular thyroid cancer is often related to the degree of vascular invasion (discussed below). Age is also an important factor in terms of prognosis. Patients over 55 year of age often have a more aggressive disease than younger patients with follicular cancer and typically the tumor does not concentrate iodine as well as in younger patients. Vascular invasion is often characteristic for follicular thyroid cancer and therefore distant metastasis is more common than in papillary thyroid cancer. Distant spread may occur even if the cancer within the thyroid is small. Lung, bone, brain, liver, bladder, and skin are potential sites of distant spread. Lymph node involvement in cases of follicular thyroid cancer is far less common (only 8-10%) compared to that of papillary thyroid cancer. Last updated January 6, 2022.

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 (~12%)
  • 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 (half of the thyroid) which contains the tumor 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 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 nearly every day.

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. Said differently, it is difficult for the pathologist to accurately diagnose follicular thyroid cancer quickly without some special preparation of the biopsy sample. 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 hemi-thyroidectomy (removing one half of the thyroid). 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. Rarely will other cells in the body 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 and therefore they can be targeted for death by giving the toxic isotope (I-131). Once again, not everybody with papillary thyroid cancer needs this therapy, but those with larger tumors, spread to lymph nodes or other areas, tumors which appear aggressive microscopically, 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 “targeted therapy” will little or no potential down-sides (no hair loss, nausea, weight loss, etc.).

Radioactive iodine uptake is enhanced by high TSH levels; thus patients should be off of thyroid hormone replacement and on a low iodine diet for at least two weeks prior to therapy. It is usually given 6 weeks post surgery (this is variable) can be repeated every 12 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?

All follicular thyroid cancer patients are followed lifelong for their disease and hormone monitoring. Patients should receive an annual blood thyroglobulin level as well as high resolution ultrasound surveillance of the neck. Serum thyroglobulin are generally not useful as a screen for the 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 structural (identifiable) recurrence even if an iodine scan is negative. Elevated thyroglobulin levels should be followed by diagnostic imaging efforts to define the potential local , regional (lymph node) or distant site analysis for structural abnormalities. Low unstimulated thyroglobulin levels in the 1-3 pg/ml may not be associated with identifiable structural disease.