Introduction
The thyroid is a small gland in the neck. It is butterfly-shaped. It produces two important hormones, T3 (triiodothyronine) and T4 (thyroxin), which regulate functions of the body like metabolism, bone growth, brain development, body temperature, menstruation, and digestion. The hypothalamus and pituitary gland located at the base of the skull are responsible for the production of thyroid hormones. The hypothalamus and pituitary complex release a hormone called TSH (thyroid-stimulating hormone) into the blood, which makes the thyroid gland release T3 and T4 into the bloodstream.
What Are the Types of Thyroid Cancers?
Thyroid cancer is of different types based on two points:
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The type of cells from which they form.
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The degree of similarity between normal cells and cancer cells.
The four main types of thyroid cancers include:
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Papillary Thyroid Cancer: Papillary thyroid cancer, or papillary carcinoma, is the most common form of thyroid cancer. It accounts for about 80 % of all thyroid carcinomas. This tumor grows forms from follicular cells in the thyroid gland and grows slowly. It can spread and affect the nearby tissues. It is a less aggressive type of thyroid cancer.
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Follicular Thyroid Cancer: The second most common thyroid cancer is follicular thyroid cancer. It accounts for around 10 % of all thyroid cancers. It occurs commonly in areas with a deficiency of dietary iodine. It is more aggressive than papillary thyroid carcinoma and can spread to nearby organs. Hurthle cell cancer is a subtype of follicular cancer and it accounts for 3 % of all thyroid cancers.
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Medullary Thyroid Cancer: Medullary thyroid cancer is more aggressive than the above two types, accounting for four percent of all thyroid cancers. Medullary cancers can spread to other body parts and have a poor prognosis.
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Anaplastic Thyroid Cancer: Anaplastic thyroid cancers are the most aggressive type that grows fast and spread to surrounding structures. They make up about 2 % of all thyroid cancers.
What Is Follicular Thyroid Carcinoma?
Follicular thyroid carcinoma is the second most common type of thyroid carcinoma. It is more aggressive than papillary cancer, as it tends to spread to nearby blood vessels and other structures. Follicular thyroid cancer affects females and whites more commonly than males and blacks. People in the age groups of 40 to 60 are commonly affected.
What Are the Symptoms of Follicular Thyroid Carcinoma?
Visible symptoms do not occur in the early stages of cancer. A lump in the neck that moves up and down while swallowing may be the first sign. The tumors are small and do not cause any discomfort in most cases. However, large tumors can cause pressure on the surrounding structures like the windpipe (trachea) and vocal cords. Pressure on the surrounding tissues can cause symptoms, which include:
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Difficulty in breathing.
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Difficulty in swallowing.
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Hoarseness of voice.
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Chronic cough.
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Paralysis of the vocal cords.
Cancers that have spread to distant parts may show symptoms based on the structure involved. For example, cancers that spread to the bone can cause bone pain or bone fractures, whereas cancers that spread to the lungs can cause breathing problems. In addition, the ability of follicular cancers to invade the blood vessels is more when compared to papillary cancers; therefore, the chance of spread is more for follicular cancers.
How Is Follicular Thyroid Carcinoma Diagnosed?
Doctors conduct a physical examination of the lump and take down the patient's history. Further, they advise tests that help diagnose the lump as cancer, which include:
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Blood tests.
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Imaging tests.
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FNAC (fine needle aspiration cytology).
Blood tests determine the levels of various hormones and minerals produced by the thyroid gland. High levels of TSH, T3, T4, calcium, calcitonin, and thyroglobulin indicate follicular cancer. However, these values may also be elevated in other thyroid conditions.
Imaging tests like ultrasound scans, radioiodine imaging, and PET-CT (positron emission tomography-computed tomography) diagnose nodules. In addition, they help determine if the lump is more or less likely to be malignant (cancerous). Chest X-rays or an MRI (magnetic resonance imaging) are done only when there is suspicion that the tumor has spread to nearby organs.
FNAC is a technique that uses a needle to withdraw cells from the lump, which are sent to a laboratory for further analysis. FNAC is the most accurate method to diagnose follicular cancer.
How Is Follicular Thyroid Carcinoma Treated?
A single or combination therapy approach is used to treat follicular cancers. Also, the treatment depends on the location and spread of the tumor. The various treatment options for follicular cancers include:
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Partial or Total Thyroidectomy: Thyroidectomy is the removal of the thyroid gland. In cases where the tumor is small and has not spread, partial thyroidectomy is preferred, in which a part of the gland having the tumor is removed. However, in bigger tumors that have spread to the nearby lymph nodes, total removal of the thyroid gland and lymph nodes is advised.
- Parathyroid glands are small pea-sized glands located behind the thyroid gland that help regulate calcium levels in the body by secreting a hormone, parathormone. During the removal of the thyroid gland, the parathyroid glands can be damaged or removed accidentally, leading to decreased calcium levels in the body. Hence, close monitoring of blood calcium levels is necessary after the surgery.
Radioactive Iodine:
Thyroid cells are the only cells in the body that can absorb iodine. They use the absorbed iodine to make the thyroid gland hormones T3 and T4. TSH is the hormone released by the pituitary gland, which stimulates the thyroid to produce hormones. Doctors take advantage of this property of the thyroid gland to absorb iodine in treating follicular cancer. Though all the patients may not require radioactive iodine therapy, older patients with large tumors spread to nearby structures may receive the treatment.
Radioactive iodine (I-131), a toxic form of iodine, is readily absorbed by the cancer cells of the thyroid, thereby destroying them. Also, I-131 works better in the presence of TSH, or a medication named Thyrogen (Thyrotropin alfa, Mannitol, Sodium Phosphate, and Sodium Chloride), which is an analog for TSH. Also, patients have to take a diet low in iodine and avoid intake of thyroid replacement hormones. This contributes to the thyroid gland's better uptake of radioactive iodine. The therapy is started about four to six weeks after thyroidectomy. There may be a few side effects of the treatment, like:
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Nausea and vomiting.
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Dryness of eyes and mouth.
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Changes in taste.
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Pain and swelling of the neck.
The body eliminates radioactive iodine through body fluids like sweat, saliva, urine, and stool. Therefore, people who receive the therapy must not stay closer to family, mainly children, as they have a chance of emitting the radioactive materials for a few days.
Other Treatment Options:
Radiotherapy (which uses high doses of radiation to kill cancer cells) and chemotherapy (which uses drugs to kill cancer cells) are the other treatment options that are rarely used to treat follicular cancers. Instead, they are used only when cancer has spread to different body parts or when they do not respond to other modes of treatment.
What Is the Follow up Care For Follicular Thyroid Carcinoma?
Doctors consider giving thyroxine, a type of thyroid replacement hormone, after total thyroidectomy, which prevents the pituitary from releasing TSH, as TSH can cause the regrowth of new thyroid tissue, particularly cancerous ones. Also, blood tests help assess the values of thyroglobulin, a thyroid tumor marker.
Conclusion
Follicular thyroid carcinoma is a type of thyroid cancer that occurs due to iodine deficiency. The outlook of the cancer is good if detected early. It is treatable in most cases, and the treatment result directly depends upon age. Post-treatment, a regular follow-up with the health care team is necessary, who carry out periodic scans to check if the tumor has any regrowth and start the treatment accordingly.
