Follicular Thyroid Cancer

Follicular thyroid cancer (FTC) is a common type of thyroid cancer, second in frequency only to papillary thyroid cancer. Like other differentiated thyroid cancers, FTC originates in the hormone-producing follicular cells of the thyroid. Located at the base of the neck, the thyroid helps regulate metabolism, growth, heart rate and body temperature. 

Unlike papillary thyroid cancer, which commonly spreads to nearby lymph nodes, follicular thyroid cancer is more likely to spread through the bloodstream to distant parts of the body, particularly the lungs and bones. When detected early, however, FTC is often highly treatable and is associated with favorable long-term outcomes.

FTC accounts for approximately 10% to 15% of all thyroid cancers. It most often affects adults between 40 and 60 years of age and occurs more frequently in women than in men. Continued advances in molecular testing, surgical techniques and targeted therapies are helping physicians tailor treatment to each patient’s needs while improving outcomes.

Causes and risk factors for follicular thyroid cancer

FTC develops when genetic alterations cause thyroid follicular cells to grow and divide uncontrollably, eventually forming a tumor. Although researchers continue to study why these mutations occur, several characteristics and environmental exposures have been associated with an increased risk. It is important to remember that many people with one or more of these risk factors never develop follicular thyroid cancer, while others who are diagnosed have no identifiable risk factors.

Some risk factors for follicular thyroid cancer cannot be changed, while others may be influenced by environmental or lifestyle factors. Nonmodifiable risk factors include:

• Age – FTC is diagnosed most often in adults between 40 and 60 years of age.
• Female sex – Women are more likely than men to develop follicular thyroid cancer.
• Inherited genetic conditions and family history – Rare hereditary syndromes and a family history of thyroid cancer may elevate the risk in some individuals.
• Certain benign thyroid conditions – Longstanding multinodular goiter and other chronic thyroid disorders are associated with an increased risk of FTC.
• History of radiation exposure – Previous exposure to ionizing radiation involving the head or neck may increase the risk of thyroid cancer, although the association is stronger for papillary thyroid cancer than FTC.

Potentially modifiable risk factors for follicular thyroid cancer include:

• Insufficient iodine intake – Iodine deficiency has historically been associated with a higher incidence of FTC, although it is uncommon in countries where iodized salt is widely used.
• Obesity – Excess body weight is associated with a modest increase in the risk of several thyroid cancers, including FTC.

Signs and symptoms of follicular thyroid cancer

FTC often develops slowly and does not cause noticeable symptoms in its earliest stages. In many cases, it is first suspected after a thyroid nodule is detected during a routine physical examination or an imaging study performed for another reason. As the tumor grows, symptoms may become more noticeable.

Symptoms of early-stage follicular thyroid cancer

When FTC symptoms occur, they may include:

• A painless lump in the front of the neck
• An enlarging thyroid nodule
• Mild swelling in the neck
• A feeling of fullness or pressure in the throat
• Enlarged lymph nodes in the neck, although this is less common with FTC than with papillary thyroid cancer

Signs of advanced follicular thyroid cancer

As FTC extends beyond the thyroid or spreads to distant organs, additional symptoms may develop, such as:

• Difficulty swallowing
• Hoarseness or other voice changes
• Difficulty breathing
• Persistent neck pain
• Bone pain or after minor injuries if the cancer has spread to the bones
• Shortness of breath or a persistent cough if the cancer has spread to the lungs
• Unexplained weight loss

How follicular thyroid cancer is diagnosed

In many cases, FTC is diagnosed after a thyroid nodule is discovered during a physical examination or imaging study. Because follicular adenomas (benign tumors) and follicular thyroid cancers can appear similar on initial testing, multiple diagnostic studies may be needed before a definitive diagnosis can be made. The physician may also order follow-up tests to determine whether the cancer has spread beyond the thyroid, which can help guide treatment planning.

The diagnostic evaluation for follicular thyroid cancer may include:

• Physical examination – The physician will examine the neck and thyroid gland for nodules, swelling and other abnormalities.
• Blood tests – Thyroid function testing can help evaluate thyroid hormone levels, although results are often normal in patients with FTC.
• Neck ultrasound – Ultrasound can assess the size and appearance of a thyroid nodule and evaluate nearby lymph nodes.
• Fine-needle aspiration (FNA) biopsy – A tissue sample is obtained from a thyroid nodule and examined under a microscope. Although FNA is the standard first-line test for evaluating thyroid nodules, it cannot always distinguish follicular thyroid cancer from a benign follicular adenoma because the entire tumor must be examined to determine whether cancer cells have invaded the thyroid capsule or nearby blood vessels.
• Diagnostic surgery – If biopsy results are indeterminate, a thyroid lobectomy may be recommended so the entire nodule can be examined under a microscope. The pathologist will evaluate whether the tumor has invaded the thyroid capsule or blood vessels, which can confirm a diagnosis of follicular thyroid cancer.
• Follow-up imaging studies – Computed tomography (CT), magnetic resonance imaging (MRI) or positron emission tomography (PET)/CT scans may be recommended if there is concern that the cancer has spread beyond the thyroid.
• Molecular testing – Genetic analysis of biopsy tissue may provide additional information that helps estimate the likelihood of cancer and guide treatment decisions in select patients.

How follicular thyroid cancer is staged

The staging process for FTC follows the American Joint Committee on Cancer (AJCC) TNM system, which considers the size of the tumor (T), any lymph node involvement (N) and the extent of cancer metastasis throughout the body (M). Unlike some cancers, however, the patient’s age at the time of diagnosis also plays a key role in follicular thyroid cancer staging.

If thyroid cancer is diagnosed before age 55, the tumor is classified as stage 1 if it remains confined to the thyroid or nearby tissues. If the cancer has traveled to distant areas of the body, it is classified as stage 2. 

If thyroid cancer is diagnosed at age 55 or older, staging depends on tumor size, whether the cancer has spread beyond the thyroid, lymph node involvement and whether distant metastases are present. In general:

• Stage 1 – The cancer remains confined to the thyroid or has only limited extension outside the thyroid without distant spread.
• Stage 2 – The cancer may involve nearby lymph nodes or show more extensive local growth, but has not spread to distant organs.
• Stage 3 – The cancer has grown into nearby structures, such as the larynx, trachea or esophagus.
• Stage 4 – The cancer has spread extensively into nearby tissues or to distant organs, such as the lungs or bones.

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How follicular thyroid cancer is treated

Treatment for FTC is tailored to the individual based on the size and extent of the tumor, the molecular characteristics of the cancer, whether any blood vessels or other surrounding tissues are involved and the patient’s overall health. Typically, care is coordinated by a multispecialty team that may include endocrine surgeons, medical oncologists, endocrinologists, radiation oncologists, radiologists and pathologists to ensure every aspect of treatment is carefully and cohesively planned.

Treatment options for follicular thyroid cancer may include:

• Surgery – FTC treatment often begins with a thyroid lobectomy or total thyroidectomy, depending on the size and extent of the tumor. Additional surgery may be considered if cancer is found after an initial lobectomy.
• Radioactive iodine (RAI) therapy – Following surgery, RAI may be used to destroy any remaining thyroid tissue or treat microscopic cancer cells that cannot be removed surgically.
• Thyroid hormone therapy – After total thyroidectomy, thyroid hormone replacement will be prescribed. This treatment may also help suppress thyroid-stimulating hormone (TSH), which can reduce stimulation of any remaining cancer cells.
• Targeted therapy – Patients with advanced, recurrent or radioactive iodine-resistant follicular thyroid cancer may benefit from targeted medications that interfere with specific molecular pathways involved in tumor growth.
• External beam radiation therapy (EBRT) – Radiation therapy may be recommended if surgery is not feasible, residual cancer remains after surgery or the tumor has spread to specific areas requiring localized treatment.
• Chemotherapy – Conventional chemotherapy is rarely used for FTC, but it may be considered in select situations if other therapies are unlikely to be effective.
• Clinical trials – Eligible patients may have access to innovative studies evaluating new targeted treatments and other emerging approaches for differentiated thyroid cancers.

The Moffitt Cancer Center difference for follicular thyroid cancer

Patients with FTC are encouraged to turn to Moffitt for coordinated care provided by specialists with extensive expertise in differentiated thyroid cancers. Using advanced imaging and molecular diagnostics, our team works together to develop individualized treatment plans based on each patient’s diagnosis, treatment goals and overall health.

As a National Cancer Institute (NCI)-designated Comprehensive Cancer Center, Moffitt also offers eligible patients access to groundbreaking clinical trials investigating promising new therapies for thyroid cancer.

If you would like to learn more about follicular thyroid cancer, you can request an appointment with a specialist in the Thyroid Clinic at Moffitt by calling 1-888-663-3488 or submitting a new patient registration form online. Virtual visits are available for patients in Florida. We do not require referrals.