Thyroid Cancer Facts

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.

About 1.1% of adults in the United States will receive a thyroid cancer diagnosis during their lifetimes, and the disease accounts for about 2.2% of all new cancer cases. Only about half a percent (0.5%) of cases are fatal, and its five-year relative survival rate is 98.4%, in part because most thyroid cancers respond well to treatment.

The American Cancer Society (ACS) estimates that in 2026:

• 45,240 new cases of thyroid cancer will be diagnosed
• 32,000 of those diagnosed will be women
• 13,240 of those diagnosed will be men

While the annual diagnostic rates of thyroid cancer increased for a time, since 2013 new thyroid cancer rates have been declining by about 1.4% per year, according to ACS. The average age at diagnosis is 51 years old, which is younger than for most cancers.

What Is Thyroid Cancer?

Cancer that begins in the cells of the thyroid gland is called thyroid cancer.

The thyroid gland is a butterfly-shaped organ of the endocrine system located in the front, lower neck area. Endocrine system organs produce and send out hormones that regulate and control many processes in the body, and thyroid hormone is the main hormone produced by the thyroid gland.

It is made up of the following active thyroid hormones:

• Triiodothyronine (T3)
• Thyroxine (T4)

Thyroid hormones help control a slew of bodily functions, including metabolism (body temperature and weight), heart rate, childhood bone growth and reproductive cycle regulation.

Thyroid cancer develops from healthy thyroid cells that change (transform) into cancerous cells. These cells divide and grow quickly and form a nodule (lump). Unless thyroid cancer is treated, the abnormal cancer cells may spread outside of the thyroid gland into nearby lymph nodes, and eventually, take over and destroy healthy tissues and organs.

The two main types of thyroid cells that thyroid cancer develops from are:

• Follicular cells, which use iodine from the blood to produce thyroid hormone
• C cells (parafollicular cells), which make another hormone produced by the thyroid called calcitonin that regulates calcium levels in the body

There are several types of thyroid cancer, each with different rates of occurrence.

Slow-growing papillary thyroid cancer (PTC) is the most common type of thyroid cancer, accounting for about 80% of diagnoses. It develops in follicular cells and tends to spread to nearby lymph nodes.

Follicular thyroid cancer (FTC) also develops from its namesake cells and tends to spread to other parts of the body more readily than PTC, but less commonly to nearby lymph nodes. It accounts for about 10% of all thyroid cancers.

Other, less common types of thyroid cancer include:

• Oncocytic thyroid cancer (formerly called Hürthle cell cancer), which is a follicular cell cancer that is more difficult to locate and treat than other forms of the disease, accounting for about 3% of thyroid cancers
• Medullary thyroid carcinoma, which is a C cell derived cancer that may spread to other organs and the lymph nodes, accounting for about 4% of thyroid cancers
• Anaplastic thyroid cancer, the most aggressive type, which may sometimes develop from an existing case of PTC or FTC, accounting for about 2% of thyroid cancers
• Rare tumors such as thyroid sarcomas (cancer that begins in soft tissue) and thyroid lymphomas (cancer that forms in cells of the immune system), which make up about 4% of thyroid cancer cases

Are All Thyroid Nodules Cancerous?

Most thyroid nodules are benign, which means they are not cancerous. About 5% to 15% of nodules found in the thyroid gland turn out to be cancer tumors.

Many thyroid nodules are sacs filled with either fluid or stored thyroid hormone known as colloid. These sacs are called cysts, and they typically are not cancerous.

If someone has thyroid nodules, cancer may be diagnosed or ruled out using tests that help the doctor determine the risk of thyroid cancer. These tests may include an ultrasound scan that takes images of the thyroid gland to check for certain structural features, such as whether the nodule is a cyst or a solid mass. Doctors may also order a biopsy, a procedure to obtain a sample of thyroid nodule tissue, which is then sent to a pathologist (a doctor trained in identifying diseases of the cells) so it can be examined under the microscope to look for thyroid cancer cells. Molecular and genetic analysis on the biopsy may be used to further help diagnose the thyroid cancer, particularly if the initial biopsy result is not conclusive.

What Causes Thyroid Cancer?

While the exact thyroid cancer causes are not yet known, certain changes (mutations) in a person’s cellular DNA may trigger healthy thyroid cells to turn into abnormal cancer cells that grow out of control.

These mutations occur in genes called oncogenes that help stimulate cell division and growth. They also sometimes occur in tumor suppressor genes that help slow down cell division and growth and trigger cell death.

In thyroid cancer, oncogene signaling may get stuck in the “on” position, while tumor suppressor signaling may get stuck in the “off” position. This allows the mutated thyroid cancer cells to overproduce and spread.

Several gene changes in the form of mutations or fusion are found in a significant portion of thyroid cancer cases. A mutation of the BRAF gene, known as BRAF V600E, is one of the most common mutations that leads to the development of papillary thyroid cancer. Another genetic change that occurs in the RET gene configuration (RET fusion) is found in about 10% to 30% of PTC cases. When these gene changes happen, they become a PTC oncogene.

RAS oncogene mutations are the most common in triggering the development of follicular thyroid carcinoma. A mutation that turns off the tumor suppressor gene called p53 is present in many anaplastic and poorly differentiated thyroid cancer diagnoses. In medullary thyroid carcinoma, both RAS and RET gene mutations are often found in the tumor cells.

Thyroid Cancer Risk Factors

Certain risk factors are associated with the development of thyroid cancer, including those listed below.

Radiation: Typically, high levels of radiation from nuclear accidents or weapons increase thyroid cancer risk, and it may also increase for those who undergo radiological imaging tests, such as X-rays, computed tomography (CT) scans or radiation treatment to the head or neck.

Gender: Women have a three times greater risk of developing thyroid cancer than men. The reason has yet to be determined.

Age: Childhood thyroid cancer is uncommon, and the disease mostly affects women in their 40s and 50s and men in their 60s and 70s.

Iodine: While follicular cell cancers tend to occur more in populations who have low levels of iodine in their diet, papillary cell cancer risk increases for those who have high iodine levels.

Body mass index (BMI): People who are overweight or obese have an increased risk of developing thyroid cancer.

Family history: People with a parent, child or sibling who have had thyroid cancer have an increased risk of developing the disease.

Hereditary conditions: Certain conditions that parents pass down to their children through genes (hereditary conditions) elevate the risk of thyroid cancer. These conditions occur due to genetic mutations.

Is Thyroid Cancer Hereditary?

The majority of thyroid cancers are not hereditary, meaning they are not due to a family history of the disease or a hereditary condition. However, a small portion of thyroid cancers are indeed hereditary.

A family history of thyroid cancer is more common for those diagnosed with medullary thyroid cancer than for those diagnosed with PTC and FTC. Familial medullary thyroid cancer occurs most often in children and young adults.

Hereditary conditions that may increase the risk of developing various types of thyroid cancer include those listed below.

Familial adenomatous polyposis (FAP): FAP is a health condition marked by a large number of colon (intestinal) polyps. It is caused by mutations in the APC gene. People with familial adenomatous polyposis are at increased risk of developing papillary thyroid cancer and other types of thyroid cancer.

Gardner syndrome: This is a subtype of FAP in which noncancerous tumors develop alongside colon polyps.

Carney complex type 1: This disorder is caused by an inherited PRKAR1A gene mutation that increases the risk for follicular and papillary cancers. It is marked by hormone issues and the development of tumors throughout the body.

Multiple hamartoma syndrome (Cowden disease): A hamartoma is an abnormal, noncancerous clump of cells and tissues formed from surrounding cells and tissues. Multiple hamartoma syndrome is sometimes called Cowden disease. The mutations to the PTEN gene that cause it may lead to a number of thyroid issues, including cancer (especially follicular and papillary cancers).

Most thyroid cancers that form as a result of gene defects are believed to develop from acquired gene alterations, in the form of mutations or fusions. This means that the gene changes were not inherited from the person’s family, but rather occurred during his or her lifetime, such as from exposure to radiation or other factors.