Most thyroid cancer is not hereditary, but some types are strongly linked to family genes

Most people who develop thyroid cancer do not inherit it from a parent. About 90 percent of thyroid cancers occur in people with no family history of the disease. However, certain types of thyroid cancer are caused by inherited genetic mutations that run through families, and if you carry one of these mutations, your risk is significantly higher than the general population.

The key distinction is between sporadic thyroid cancer (occurring randomly, without a genetic cause) and hereditary thyroid cancer (caused by a gene mutation passed down through your family). Knowing which type affects your family changes what screening and prevention steps make sense for you and your relatives.

Key Takeaways

  • Hereditary medullary thyroid cancer is caused by mutations in the RET gene and accounts for about 25 percent of all medullary thyroid cancers.
  • If you have a family history of medullary thyroid cancer or multiple endocrine neoplasia (MEN) syndromes, genetic testing can reveal whether you carry the mutation.
  • People who inherit the RET mutation have a very high lifetime risk of developing medullary thyroid cancer, sometimes before age 40.
  • Genetic counseling before and after testing helps you understand what results mean for your health and your family members' health.
  • Preventive surgery to remove the thyroid is an option for people who carry the hereditary mutation but have not yet developed cancer.

The two main hereditary forms of thyroid cancer

Hereditary medullary thyroid cancer (HMTC) is the most common inherited form. It is caused by mutations in the RET gene, which normally helps control cell growth. People who inherit a mutated RET gene have a 50 percent chance of passing it to each child, and nearly all carriers will develop medullary thyroid cancer at some point in their lives if the cancer is not prevented surgically.

Familial adenomatous polyposis (FAP) is a syndrome caused by mutations in the APC gene. People with FAP develop hundreds of polyps in the colon and have a higher risk of several cancers, including thyroid cancer (usually papillary type). FAP is less common than hereditary medullary thyroid cancer but affects multiple organs.

A third hereditary syndrome, Cowden syndrome, caused by PTEN gene mutations, also increases thyroid cancer risk, though it is rare. These syndromes often come with other health conditions—for example, hereditary medullary thyroid cancer is sometimes part of a larger condition called multiple endocrine neoplasia type 2 (MEN2), which also affects the adrenal glands and parathyroid glands.

How doctors identify hereditary thyroid cancer in your family

Your doctor will ask detailed questions about your family's medical history, looking for patterns: Did a parent, sibling, or child develop thyroid cancer? At what age? Did they have medullary type specifically? Did other family members have cancer or endocrine disorders? This conversation is called risk assessment, and it helps determine whether genetic testing makes sense for you.

If your family history suggests a hereditary form, your doctor will refer you to a genetic counselor—a healthcare professional trained to explain how genes work, what testing involves, and what results mean. The counselor reviews your family tree, discusses the pros and cons of testing, and answers questions before you decide whether to proceed.

Genetic testing itself is straightforward: a blood sample or saliva sample is sent to a laboratory, where technicians look for mutations in the RET gene (for medullary thyroid cancer) or other genes linked to thyroid cancer risk. Results typically come back within two to four weeks. A positive result means you carry the mutation; a negative result means you do not carry the specific mutation being tested for.

What a positive genetic test means for your health

If you test positive for a RET mutation, your lifetime risk of developing medullary thyroid cancer is very high—often 90 percent or higher. However, "high risk" does not mean you have cancer now. It means your cells carry the mutation and cancer is likely to develop unless you take preventive action.

The timing varies. Some people develop medullary thyroid cancer in childhood; others do not show signs until adulthood. Your doctor will recommend regular screening with blood tests (measuring calcitonin levels, a hormone produced by thyroid cells) and ultrasound imaging of the thyroid. How often you are screened depends on your age and your specific RET mutation—some mutations are more aggressive than others.

Many people with a RET mutation choose prophylactic thyroidectomy—surgical removal of the thyroid before cancer develops. This is a major decision and is usually discussed with your doctor, genetic counselor, and sometimes an endocrinologist (a hormone specialist). The surgery prevents medullary thyroid cancer almost entirely, but it means lifelong thyroid hormone replacement therapy and the surgical risks that come with any operation.

What happens if you test negative

A negative genetic test result is reassuring but does not eliminate all thyroid cancer risk. It means you do not carry the specific hereditary mutation your family is known to have. You still have the same thyroid cancer risk as the general population, which is low.

However, if your family has a known mutation and you test negative, you do not need the intensive screening or preventive surgery that mutation carriers require. You can follow standard health guidelines for cancer screening and report any new symptoms (like a lump in the neck or difficulty swallowing) to your doctor promptly.

Genetic testing and what it costs

Genetic testing for thyroid cancer risk is usually ordered by your doctor and performed at a specialized laboratory. The cost varies depending on which genes are tested and your insurance coverage. Many insurance plans cover genetic testing when there is a documented family history of hereditary thyroid cancer or when a doctor orders it for medical reasons.

If cost is a concern, ask your doctor's office or the genetic counselor whether the laboratory offers financial assistance or sliding-scale fees. Some academic medical centers and cancer centers offer testing at reduced cost or free of charge to people who meet certain criteria.

Telling your family members

If you test positive for a hereditary thyroid cancer mutation, your blood relatives—parents, siblings, and children—have a 50 percent chance of carrying the same mutation. Genetic counselors and doctors recommend that you share this information with them so they can decide whether to pursue testing themselves.

This conversation can be difficult. A genetic counselor can help you prepare what to say and can sometimes speak with family members directly if you request it. The goal is to give relatives the information they need to make informed decisions about their own health, not to alarm them. Many families find that knowing the risk allows them to take control through screening or prevention.

Frequently Asked Questions

Can I develop thyroid cancer if I test negative for the RET mutation?

Yes. A negative test means you do not carry the hereditary mutation your family has, but you can still develop sporadic (non-hereditary) thyroid cancer. Your risk is the same as anyone else's—low overall, but not zero. Report any neck lumps or symptoms to your doctor.

If my parent has hereditary medullary thyroid cancer, do I definitely have it too?

No. You have a 50 percent chance of inheriting the RET mutation from a parent who carries it. The only way to know is through genetic testing. Even if you inherit the mutation, you may not develop cancer until later in life, or preventive surgery may prevent it entirely.

What is the difference between medullary and papillary thyroid cancer?

Medullary thyroid cancer develops from cells that produce calcitonin (a hormone), while papillary thyroid cancer develops from follicular cells that produce thyroid hormone. Medullary type is the one most often hereditary. Papillary is more common overall but is usually sporadic unless it occurs as part of a syndrome like FAP.

Do I need genetic testing if no one in my family has had thyroid cancer?

Probably not, unless you have been diagnosed with medullary thyroid cancer yourself or have another condition (like MEN2) that increases risk. Genetic testing is most useful when there is a known family history. Talk to your doctor about your personal risk.

How often should I be screened if I carry a RET mutation?

Screening frequency depends on your age and your specific mutation. Children and young adults with aggressive mutations may be screened every few months; others may be screened annually. Your endocrinologist will set a schedule based on your individual risk and will adjust it as you age.