Follicular Thyroid Cancer

June 15, 2024 
This page was reviewed under our medical and editorial policy by Sasan Fazeli, M.D., assistant clinical professor in the Department of Diabetes, Endocrinology and Metabolism, and Karen Tsai, M.D., assistant clinical professor in the Department of Diabetes, Endocrinology and Metabolism, City of Hope^® Cancer Center Duarte.

Follicular cells are one of two types of cells found in the thyroid gland. These cells produce thyroid hormones, which are essential to regulating multiple processes throughout the body. Several different types of cancer may develop from these follicular cells.

The second-most common of these cancers is follicular thyroid cancer. Health care providers may also call it follicular thyroid carcinoma or follicular thyroid adenocarcinoma. This type of thyroid cancer accounts for about 10% of all cases of thyroid cancer.

What Is Follicular Thyroid Cancer?

Follicular thyroid cancer is a disease in which cancer cells form in the thyroid’s follicular cells. It is considered a type of well-differentiated cancer, which means that cells taken from follicular thyroid tumors have well-developed structures inside them that look more like normal thyroid cells.

Well-differentiated cancers tend to grow and spread more slowly than other types of cancer that are poorly differentiated or undifferentiated.

Due to this characteristic, follicular thyroid cancer tends to be more responsive to treatment.

Metastatic Follicular Thyroid Cancer

Health care providers use cancer staging to describe the characteristics of cancer, recommend treatments and form a prognosis. During the thyroid cancer staging process, they use information about the size of the tumor, whether nearby lymph nodes are involved and whether the cancer has metastasized (spread) to other areas of the body. Additionally, follicular thyroid cancer stages also take into account the age at which the person is diagnosed.

Follicular cancer typically grows slowly and does not usually spread to the lymph nodes. For this reason, follicular thyroid cancer that has metastasized in patients under the age of 55 is considered Stage 2. In patients who are 55 years of age or older, it is considered Stage 4.

When follicular thyroid cancer does spread to other areas of the body, the most common sites are the lungs and bones.

Follicular Thyroid Cancer Symptoms

Not all patients with follicular thyroid cancer experience symptoms. Many cases of thyroid cancer are only found when a health care provider notices a lump in the throat on a physical exam or when the patient has an imaging scan for another reason.

When symptoms are present, they may include:

• A lump near the Adam’s apple
• Swollen glands in the neck
• Trouble breathing
• Trouble swallowing
• A hoarse voice
• Pain in the throat
• A persistent cough
• Neck enlargement

Patients who experience any of these symptoms should make an appointment with a health care provider to receive an appropriate diagnosis and treatment recommendations.

What Causes Follicular Thyroid Cancer?

While researchers do not know the exact cause of follicular thyroid cancer, they have found links between developing the disease and:

• Exposure to radiation
• Family history of thyroid cancer in first-degree relatives
• Iodine intake (both too much and too little)
• Obesity
• Diabetes
• Hashimoto’s thyroiditis (an autoimmune disorder)

People in certain occupations have also been found to have a higher likelihood of developing follicular thyroid cancer. This includes people who have exposure to radiation or pesticides or who work in the textile industry.

Follicular Thyroid Cancer Diagnosis

When the thyroid care team suspects thyroid cancer, they may perform several different types of tests to confirm the diagnosis and determine whether the cancer has spread. These tests may include:

• A physical exam
• An ultrasound
• Blood tests to look at thyroid hormone levels or tumor marker levels
• A biopsy to sample a piece of the thyroid nodule and examine it under a microscope
• A computed tomography (CT) scan or a positron emission tomography (PET) scan to determine whether the cancer has spread to other areas of the body

Not every type of test will be used for every patient. Examining the cells under a microscope after a biopsy and/or surgery is the primary way to confirm a diagnosis of follicular thyroid cancer.

Follicular Thyroid Cancer Treatment

Treatment options available for follicular thyroid cancer depend on the stage of the cancer when diagnosed. They include those listed below.

Surgery: Depending on the size and spread of the tumor, all or part of the thyroid may be surgically removed (total or partial thyroidectomy).

Radioactive iodine therapy (RAI): The thyroid gland absorbs iodine. Doctors may give patients a dose of radioactive iodine, which will be absorbed by the thyroid and thyroid cancer cells to destroy them with minimal impact on the rest of the body. This may destroy thyroid tissue that was missed during surgery or cancer cells that spread to nearby lymph nodes.

Radiation therapy: For patients whose thyroid cancer has metastasized, high-energy X-rays may be used to target and destroy tumors in the bones and soft tissues where they might have spread.

Targeted therapy: These oral drugs specifically target mutations or fusions within the cancer cell that help it to develop cancerous properties. These drugs may block proteins that help cancer cells grow.

For follicular cancer, different types of targeted drugs may be used. These treatments are typically considered if there’s evidence of metastatic disease or imminently threatening disease not otherwise amenable to local control, surgery or other approaches.

Before starting these treatments, a comprehensive molecular analysis on the tumor tissue is essential, which helps in selecting the appropriate targeted therapy type, which may include multikinase inhibitors, BRAF inhibitors, RET inhibitors, TRK inhibitors and ALK inhibitors.

Immunotherapy: Immunotherapy medications are administered as infusions, typically as second-line treatments if the initial targeted therapies are failing.

Chemotherapy: Drugs that destroy or stop the growth of cancer cells may be used to help stop tumors from progressing.

Follicular Thyroid Cancer Survival Rate

Follicular cancer survival rates are estimates based on the percentage of patients with the same stage of cancer who were still alive five years or more after their cancer diagnosis. They are based on outcomes of a large number of people in the past. These rates may give patients and providers an idea about how successful treatment might be, but they do not predict how an individual patient will fare.

The American Cancer Society reports that the five-year relative survival rate for follicular thyroid cancer is:

• More than 99.5% for patients with cancer that has not spread outside the thyroid
• 98% if cancer has spread to nearby areas
• 67% if cancer has metastasized to distant areas of the body

Patients and their families should be aware that thyroid cancer treatments are improving over time. Clinical trials are being conducted, which may lead to even more potential treatments for advanced cancers than were available in the past.