Thyroid Cancer: Follicular Cancer
The Second Most Common Type of Thyroid Cancer
Follicular thyroid cancer is the second most common type of thyroid cancer (papillary thyroid cancer is the most common thyroid cancer). This article will focus on the symptoms, diagnosis, and treatments for follicular thyroid cancer. You can read our Introduction to Thyroid Cancer article for an overview of the various types of thyroid cancer.
Learn more about thyroid cancer in our Patients' Guide to Thyroid Cancer. It covers diagnosis and treatments for all types of thryoid cancer, including follicular thyroid cancer.
About 15% of all thyroid cancer cases are follicular thyroid cancer.1 Follicular carcinoma is considered more malignant (aggressive) than papillary carcinoma.
But what are some common follicular thyroid cancer symptoms, and how is follicular thyroid cancer diagnosed? Follicular thyroid cancer occurs in a slightly older age group than papillary thyroid cancer 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 older than 40 years old 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.
With follicular thyroid cancer, lung, bone, brain, liver, bladder, and skin are potential sites of distant spread. Lymph node involvement is far less common than in papillary carcinoma.
Characteristics of Follicular Thyroid Cancer
- Peak onset of follicular thyroid cancer is between ages 40 and 60 years old.
- Follicular thyroid cancer is more common in females than males by 3:1 ratio.
- The prognosis directly related to tumor size (less than 1.0 cm [3/8 inch] is a good prognosis).
- This cancer is rarely associated with radiation exposure.
- Cancer that spreads to lymph nodes is uncommon (~10%) in follicular thyroid cancer.
- Invasion into vascular structures (veins and arteries) within the thyroid gland is common.
- Distant spread (to lungs or bones) is uncommon, but it is more common than with papillary cancer.
- Overall cure rate is high (near 95% for small lesions in young patients), but this decreases with 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 that 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 despite the fact that small amounts of tumor cells can be found in up to 88% of the opposite lobe thyroid tissues.
The other side of the controversy is a total thyroidectomy. This is a more aggressive surgery.
But what are some common follicular thyroid cancer treatments? The following is a typical plan for treating follicular thyroid cancer: Follicular carcinomas that are well circumscribed, isolated, minimally invasive, and less than 1 cm in a young patient (younger than 40 years old) may be treated with hemi-thyroidectomy 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 our surgical options article.
Radioactive Iodine for Follicular Thyroid Cancer
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 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 that appear aggressive microscopically, tumors that invade blood vessels within the thyroid, and older patients may benefit from this therapy. This is extremely individualized, and your doctor will make the best recommedation for your case. 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 thyroid-stimulating hormone (TSH) levels; thus patients should be off of thyroid replacement and on a low iodine diet for at least 1 to 2 weeks prior to therapy. It is usually given 6 weeks post-surgery (although this can vary) and can be repeated every 6 months if necessary (within certain dose limits).
Thyroid Hormone Replacement for Follicular Thyroid Cancer
Regardless of whether a patient has just one thyroid lobe and the isthmus removed, or the entire thyroid gland removed with a total thyroidectomy, most experts agree these patients should be placed on thyroid hormone for the rest of their lives.
This is to replace the missing hormone in those who have had the thyroid gland removed and to suppress further growth of the gland in those with some tissue left in the neck. There is good evidence that follicular carcinoma (such as papillary cancer) responds to TSH secreted by the pituitary, therefore, exogenous thyroid hormone is given. This results in decreased TSH levels and a lower impetus for any remaining cancer cells to grow.
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 a check of thyroglobulin levels. Thyroglobulin is not useful as a screen for initial diagnosis of thyroid cancer, but it is 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 indicative of recurrence. A value of greater than 10 ng/ml is often associated with recurrence even if an iodine scan is negative.
Follicular Thyroid Cancer Conclusion
Talk to your doctor about any concerns you have about follicular thyroid cancer, including which treatments are an option for you. Be sure to keep track of all your follicular thyroid cancer symptoms so you can discuss them with your doctor.