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The Genetics of Thyroid Cancer: What You Need to Know

Thyroid cancer is a common and mostly treatable disease, though there are some aggressive forms of thyroid cancer that do not respond to treatment.  About 63,000 Americans will be diagnosed with thyroid cancer and nearly 2,000 people will die of the disease in 2014, according to the American Cancer Society.

As a genetic counselor who specializes in cancer, I study thyroid cancer and regularly meet with thyroid cancer patients and their families.  Here I explain the different types of thyroid cancer, the role genetics plays and what you should know if you or a family member has the disease.

The thyroid is a gland in the neck area that secretes hormones that regulate many of your body's functions, including growth and development, metabolism and body temperature.  There are many types of thyroid cancer and we don't know the causes of all of them. One of the more aggressive types, called medullary thyroid cancer, is often hereditary and genetic testing can and should be performed.

Even if you have a type of thyroid cancer for which there is no test, it's a good idea to ask your doctor about meeting with a genetic counselor. Since thyroid cancer can sometimes run in families, a genetic counselor can examine your family history and advise you and your relatives on your risk and how that might affect how you and your doctor monitor and manage your health.  Here are some of the specific types of thyroid cancer and what we know about them.

The Genetics of Thyroid Cancer: What You Need to Know

Thyroid cancer is a common and mostly treatable disease, though there are some aggressive forms of thyroid cancer that do not respond to treatment.  About 63,000 Americans will be diagnosed with thyroid cancer and nearly 2,000 people will die of the disease in 2014, according to the American Cancer Society.

As a genetic counselor who specializes in cancer, I study thyroid cancer and regularly meet with thyroid cancer patients and their families.  Here I explain the different types of thyroid cancer, the role genetics plays and what you should know if you or a family member has the disease.

The thyroid is a gland in the neck area that secretes hormones that regulate many of your body's functions, including growth and development, metabolism and body temperature.  There are many types of thyroid cancer and we don't know the causes of all of them. One of the more aggressive types, called medullary thyroid cancer, is often hereditary and genetic testing can and should be performed.

Even if you have a type of thyroid cancer for which there is no test, it's a good idea to ask your doctor about meeting with a genetic counselor. Since thyroid cancer can sometimes run in families, a genetic counselor can examine your family history and advise you and your relatives on your risk and how that might affect how you and your doctor monitor and manage your health.  Here are some of the specific types of thyroid cancer and what we know about them.

Papillary and Follicular Thyroid Cancer

The most common form of thyroid cancer is papillary thyroid cancer or PTC, which accounts for more than 80 percent of all thyroid cancer cases.  PTC is three times more common in women and is increasing in incidence more rapidly than all cancers worldwide.  The second most common form of thyroid cancer is called follicular thyroid cancer, or FTC and it accounts for approximately 10 percent of all cases. Most people with these two types of thyroid cancer can be cured with surgery and/or  radioactive iodine therapy , in which the iodine is ingested in liquid or capsule form and destroys the thyroid gland and other cancer cells with little effect on the rest of the body.

The genetics of papillary and follicular thyroid cancer are complex and not well-understood. We know that genes play an important role in PTC and FTC because people who have a close family member with the disease are 4 to 8 times more likely to get thyroid cancer themselves. There are a number of hereditary syndromes that increase your likelihood of developing several types of cancer, including thyroid cancer,  but these conditions are extremely rare and most people with PTC or FTC do not have one of these syndromes.

PTC and FTC can also occur in a condition known as familial non-medullary thyroid cancer or FNMTC. FNMTC is defined as two or more cases of PTC or FTC in close family members (parents, siblings or children). In these families, the risk of thyroid cancer may be quite high. The causes of FNMTC are   complex, with many genetic mutations plus environmental factors likely playing a role.  To date, most of the mutations that cause FNMTC are unknown and there is currently no genetic testing for this condition.  But the hope is that researchers will eventually identify the major genetic cause(s) so that a test can be developed.

Medullary and Anaplastic Thyroid Cancer

Two of the more aggressive forms of the disease, medullary thyroid cancer (MTC) and anaplastic thyroid cancer, account for only 5 percent to 7 percent of all cases, but have poor survival especially when diagnosed at a late stage.

Medullary thyroid cancer is strongly associated with an inherited syndrome called MEN 2 that causes benign and cancerous tumors of several glands, including the thyroid. Approximately one out of every four people with MTC has this syndrome, which is caused by a genetic mutation. Because of this, genetic counseling and genetic testing are recommended for any individual diagnosed with MTC regardless of age or family history. It's also recommended in those who have a personal or family history the types of tumors associated with MEN 2. Diagnosing MEN 2 in a family can lead to earlier detection and risk reduction in those with the condition.  

Genetic Counseling

It is important for you to let your doctor know if you have a family history because many healthcare providers are not aware that the more common forms of thyroid cancer can also run in families. If you have thyroid cancer or a family history of the disease you should talk to your doctor about seeing a genetic counselor to determine if genetic testing is appropriate for you.  Especially if:

  • You or a family member has the medullary form, which is both more aggressive and associated with a known genetic cause.
  • You or a family member has MEN 2, which  causes benign and cancerous tumors of endocrine glands
  • You have a family history of FNMTC, a condition in which two or more family members have the most common form s of thyroid cancer.

Even if there isn't a genetic test to identify the form of thyroid cancer you or a family member has, it is important to meet with a genetic counselor to assess your family history and help you and your doctor understand your risk and help you communicate that risk to other family members. Find a genetic counselor in your area by using NSGC's “ Find a Genetic Counselor ” tool. For more information about thyroid cancer visit thyca.org .

Rebecca Nagy, MS, CGC , is the immediate past president of the National Society of Genetic Counselors, and Clinical Associate Professor of Internal Medicine at The Ohio State University's Wexner Medical Center in Columbus, Ohio.