Follicular Thyroid Cancer
Follicular thyroid cancer is the second most common type of thyroid cancer, accounting for about 10 to 15% of all thyroid cancer cases. Despite being classified as a well-differentiated cancer, it is generally more aggressive than papillary thyroid cancer and has a greater tendency to spread through the bloodstream to distant organs. However, with proper treatment, particularly when diagnosed early, follicular thyroid cancer is highly treatable and often curable, with overall cure rates approaching 95%.
Table of contents
- What is follicular thyroid cancer?
- Where it develops
- Who is affected
- Signs and symptoms
- Causes and risk factors
- How it is diagnosed
- Treatment options
- Outlook and survival
- Living with follicular thyroid cancer
What is follicular thyroid cancer?
Follicular thyroid cancer is a type of cancer that develops in the thyroid gland, a butterfly-shaped organ located at the base of your neck. The thyroid produces hormones that help control your body’s metabolism (the process by which your body converts food into energy), heart rate, blood pressure, and body temperature[1].
This cancer is called “follicular” because it develops in the follicular cells of the thyroid gland. These are cuboidal epithelial cells that line small round structures called follicles, which are the functional and structural units of the thyroid[3]. These cells are responsible for producing and releasing thyroid hormones, namely T3 and T4[4].
Follicular thyroid cancer is classified as a “well-differentiated” thyroid cancer, which means the cancer cells still resemble normal thyroid cells when examined under a microscope. This classification is important because well-differentiated cancers are generally more treatable and often curable[1]. However, follicular thyroid cancer is typically a bit more aggressive than papillary thyroid cancer, the most common type of thyroid cancer[2].
Where it develops
- Thyroid gland
- Neck
- Follicular cells
The thyroid gland sits just below the cricoid cartilage (a ring-shaped piece of cartilage in your neck) and is composed of a right lobe and a left lobe separated by a thin piece of tissue called the isthmus[3]. A characteristic feature of follicular carcinoma is the formation of small follicles or hollow round structures within the thyroid tissue[4].
One of the defining features of follicular thyroid cancer is its ability to invade blood vessels and the capsule surrounding the thyroid. This vascular invasion (invasion into veins and arteries) is often characteristic of follicular thyroid cancer and allows cancer cells to spread to distant parts of the body more easily than papillary thyroid cancer[2].
Who is affected
Follicular thyroid cancer makes up between 10% and 15% of all thyroid cancers in the United States[1][3]. Anyone can develop this type of cancer, but it occurs more often in older women[1].
The cancer typically affects people in a slightly older age group than papillary thyroid cancer does, with peak onset between ages 40 and 60[2][15]. Women are more commonly affected than men by a ratio of 3 to 1[2][15]. Follicular thyroid cancer is also less common in children compared to other types of thyroid cancer[2].
Signs and symptoms
Many people with follicular thyroid cancer do not have any symptoms, especially in the early stages[4]. When symptoms do occur, they may include:
- A painless lump on the front of your neck, also called a thyroid nodule[1][4]
- An enlarged thyroid gland[4]
- Pain in the ear, jaw, or neck[1][4]
- Hoarseness or voice changes[1][4]
- Swollen lymph nodes in the neck[1]
- Trouble breathing[1][4]
- Trouble swallowing, also called dysphagia[1]
Many of these symptoms can also be caused by noncancerous conditions affecting the thyroid gland, such as inflammation. If you notice any of these symptoms, it is important to schedule an appointment with your healthcare provider. Early detection is crucial to increasing the success of treatment[4].
Causes and risk factors
Follicular thyroid cancer happens when cells in the thyroid gland grow in abnormal ways. Healthcare providers do not always know exactly why these cancers occur[1].
Several factors can increase the risk of developing follicular thyroid cancer:
- Radiation exposure: Thyroid cancer is more common in people who have been exposed to high levels of radiation, such as those who received radiation therapy to the head or neck for other cancers, or who work near radiation. After the 1986 Chornobyl explosion, many radiation-induced cancers were observed, including thyroid cancer[1][3]. However, follicular thyroid cancer occurs only rarely after radiation exposure, in contrast to papillary thyroid cancer[2].
- Iodine deficiency: Areas with low iodine in the diet have higher rates of follicular thyroid cancer[3][15].
- Age and sex: Being female and over 55 years of age are important risk factors. Patients over 55 often have more aggressive disease than younger patients[2].
- Family history: A strong family history of thyroid cancer or certain thyroid cancer syndromes can increase risk[15].
- Obesity: Being significantly overweight may increase the risk[3][15].
- Other conditions: Conditions such as diabetes, Hashimoto thyroiditis, and dietary choices have been linked to increased risk[3].
Genetic changes also play a role. Up to half of follicular carcinoma cases show RAS point mutations, while about one-third show PAX-PPAR-gamma rearrangements[3]. Mutations in genes like HRAS, NRAS, KRAS, MINPP1, and PTEN have also been observed[7].
Follicular thyroid cancer is not contagious and cannot be passed from one person to another[1].
How it is diagnosed
Diagnosing follicular thyroid cancer can be challenging because it is difficult to distinguish between follicular adenoma (a benign tumor) and follicular carcinoma based solely on the examination of cells under a microscope[6][7]. In fact, follicular adenomas occur more commonly than follicular carcinomas, with a ratio estimated to be 5 to 1[3].
The diagnostic process typically involves several steps:
Physical examination: Your doctor will feel your neck for any lumps or nodules on the thyroid gland and check for swollen lymph nodes[4].
Blood tests: These measure thyroid hormone levels and other substances to check thyroid function[1][4].
Ultrasound: This imaging test uses sound waves to create detailed pictures of the thyroid, helping determine the size, shape, and characteristics of any nodules[1][4].
Fine-needle aspiration (FNA) biopsy: A thin needle is inserted into the lump on your neck to extract cells for examination under a microscope[1][4]. However, FNA cannot definitively distinguish between benign follicular adenoma and malignant follicular carcinoma[7].
Core needle biopsy: If the fine needle aspiration results are inconclusive, your doctor may use a larger needle to obtain more tissue[4].
Surgery and pathological examination: Because it is impossible to distinguish between follicular adenoma and carcinoma on cytological grounds, a surgical procedure to remove all or part of the thyroid gland may be necessary to obtain sufficient tissue for a definitive diagnosis. Features required for the diagnosis of follicular carcinoma include capsular invasion (cancer growing through the fibrous capsule surrounding the thyroid) and vascular invasion by tumor cells[6][7].
Additional imaging tests such as CT scans, MRI, or other scans may be done to determine if the cancer has spread to other parts of the body[1][4].
Treatment options
The treatment for follicular thyroid cancer depends on several factors, including the size and stage of the cancer, whether it has spread to other parts of the body, your overall health, and your treatment preferences[1][4].
Surgery
Surgery is the primary and most common treatment for follicular thyroid cancer[11][12][15]. The type of surgery depends on the size of the tumor and whether the cancer has spread:
- Lobectomy: Removal of one lobe (half) of the thyroid. This may be used initially to confirm a diagnosis of follicular thyroid cancer[12]. Current guidelines recommend lobectomy plus removal of the isthmus as the initial surgery for patients with follicular neoplasms[6][8].
- Completion thyroidectomy: Removal of the remaining thyroid after lobectomy, performed if the pathology confirms follicular thyroid cancer[7][12].
- Total thyroidectomy: Removal of the entire thyroid gland. This is commonly used to treat follicular thyroid cancer, particularly for cancers that are large, located in both halves of the thyroid, or have spread to lymph nodes[4][12][15].
- Neck dissection: Removal of lymph nodes from the neck. This is done if there is evidence that cancer has spread to the lymph nodes, though this is less common with follicular thyroid cancer than with papillary thyroid cancer[2][12].
It is critical that all of the follicular thyroid cancer is removed from the neck in the initial surgery. Expert evaluation and complete removal of all cancer with the first surgery are extremely important to avoid complications and leaving cancer behind[11][15].
Radioactive iodine therapy
About 4 to 6 weeks after surgical thyroid removal, patients may receive radioactive iodine (RAI) therapy[8]. This treatment uses a pill or liquid containing radioactive iodine to destroy any remaining thyroid tissue or cancer cells after surgery[4]. This is particularly effective for follicular thyroid cancer because follicular cells absorb iodine[4].
RAI therapy may be used after surgery to treat any cancer cells or thyroid tissue that remains, or to treat cancer that has spread to lymph nodes or other parts of the body[12]. However, in older patients (over 55 years), the tumor may not concentrate iodine as well as in younger patients[2].
Thyroid hormone replacement therapy
After a total thyroidectomy, you will need to take a synthetic thyroid hormone pill daily for the rest of your life to replace the hormones your thyroid gland used to produce[1][4]. This treatment typically involves taking 2.5 to 3.5 micrograms per kilogram of body weight of levothyroxine (L-T4) every day[8]. The thyroid hormone is given in a dose necessary to suppress thyrotropin (also called TSH, a hormone that stimulates the thyroid) to a value of 0.1 to 0.5 milli-units per liter[8]. This helps prevent the growth of any remaining cancer cells.
External radiation therapy
If all visible cancer cannot be removed during surgery, or if residual disease does not respond to radioactive iodine, external beam radiation therapy may be used[8][12]. This involves using high-energy rays or particles from outside the body to destroy cancer cells. Radiation therapy is indicated for unresectable disease extending into adjacent structures such as the trachea, esophagus, or blood vessels[8].
Targeted therapy and chemotherapy
For advanced or metastatic follicular thyroid cancer that no longer responds to radioactive iodine, targeted therapies such as tyrosine kinase inhibitors may be considered[6][8]. Chemotherapy may be considered in symptomatic patients with recurrent or progressive disease and could improve quality of life in patients with bone metastases[6].
Outlook and survival
The prognosis for most patients with follicular thyroid cancer is excellent[1]. Follicular thyroid cancer is highly treatable and often curable, with overall cure rates approaching 95%, particularly for small tumors in young patients and when treated by expert surgeons at specialized, high-volume thyroid centers[2][15].
Survival rates depend on several factors, including the size of the tumor, whether it has spread, and the age of the patient:
- The 5-year survival rate for follicular thyroid cancer that has not spread outside of the thyroid gland is almost 100%[15].
- The 5-year survival rate for cancer that has only spread to lymph nodes or tissue in the neck is 98%[15].
- For cancer that has spread to distant parts of the body (metastatic disease), the 5-year survival rate is 63%[15].
- Overall, around 85 out of every 100 men and 90 out of every 100 women survive thyroid cancer for at least 5 years after diagnosis[20].
- Ten-year survival rates for follicular thyroid cancer are also very high, with around 85 out of every 100 people surviving 10 years or more after diagnosis[20].
Several factors affect prognosis:
- Tumor size: Prognosis is directly related to tumor size. Tumors less than 1.0 centimeter have a good prognosis[2].
- Age: Age is an important factor. Patients over 55 years of age often have more aggressive disease than younger patients[2].
- Vascular invasion: Death from follicular thyroid cancer is often related to the degree of vascular invasion[2].
- Metastasis: Distant spread to organs such as lungs, bones, brain, liver, bladder, or skin can occur even if the cancer within the thyroid is small[2]. About 11% of patients with follicular thyroid cancer have metastases beyond the neck on initial presentation[6].
Lymph node involvement in cases of follicular thyroid cancer is far less common (only 8 to 10% to 12%) compared to papillary thyroid cancer[2][6]. However, spread to other organs through the bloodstream is more common than in papillary thyroid cancer[2].
Living with follicular thyroid cancer
After treatment for follicular thyroid cancer, ongoing monitoring and care are essential. Your healthcare provider will recommend regular follow-up appointments to check for any signs of cancer recurrence[1].
A 10-year recurrence rate of 20% to 30% may be seen in older patients, in patients with primary tumors greater than 4 centimeters in diameter, and in patients where tumor has spread beyond the thyroid boundaries and where lymph node involvement is widespread[8].
After surgery, you will need to take thyroid hormone replacement therapy for life. This involves taking a daily pill to replace the hormones your thyroid used to make[1][4]. Regular blood tests will be needed to ensure you are receiving the correct dose.
Managing side effects from treatment is an important part of survivorship. Surgery can sometimes affect the parathyroid glands (which control calcium levels) or the nerves to the voice box. Radioactive iodine therapy may cause temporary side effects[2]. Your healthcare team can help you manage these effects.
Emotional and psychological support is also important. A cancer diagnosis can be stressful, even when the prognosis is excellent. Consider joining a support group or speaking with a counselor if you are struggling with anxiety or depression.
It is essential to be involved in your care decisions and to communicate openly with your healthcare team about any concerns or symptoms you experience. Early detection of any recurrence improves the chances of successful treatment.
