Research indicates a possible relationship between breast and thyroid cancers. A history of breast cancer may increase your risk for thyroid cancer. And a history of thyroid cancer may increase your risk for breast cancer.

Several studies have shown this association but it’s unknown why this potential connection exists. Not everyone who’s had one of these cancers will develop the other, or second, cancer.

Keep reading to learn more about this connection.

Researchers looked at 37 peer-reviewed studies containing data on the relationship between breast and thyroid cancers.

They noted in a 2016 paper that a woman who’s had breast cancer is 1.55 times more likely to develop a second cancer of the thyroid than a woman without a history of breast cancer.

A woman with thyroid cancer is 1.18 times more likely to develop breast cancer than a woman without a history of thyroid cancer.

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Researchers are unsure about the connection between breast and thyroid cancers. Some research has indicated the risk of developing a second cancer increases after radioactive iodine is used to treat thyroid cancer.

Iodine is generally considered safe, but it could trigger a second cancer in a small number of people. Radiation used to treat certain forms of breast cancer may increase the risk of developing thyroid cancer.

Certain genetic mutations like a germline mutation could link the two forms of cancer. Lifestyle factors like exposure to radiation, poor diet, and lack of exercise, could also increase the risk of both cancers.

Some researchers also noted the possibility of a “surveillance bias,” which means a person with cancer is more likely to follow up with screening after treatment. This improves detection of a secondary cancer.

That means a person with breast cancer may be more likely to get screened for thyroid cancer than someone without a history of cancer. Also, a person with thyroid cancer may be more likely to be screened for breast cancer than someone without a history of cancer.

A 2016 study suggests that surveillance bias was unlikely the reason for increased incidence in second cancers in people with a history of breast cancer. The researchers left out people who were diagnosed with the second cancer within a year of their primary cancer diagnosis.

They also analyzed the results by dividing the data into groups based on the time between the diagnosis of the first and the second cancer.

An earlier study also used the time between the diagnosis of the first and second cancers to conclude that surveillance bias was unlikely to account for increased incidence of a second cancer in people who’ve had thyroid cancer.

Both breast and thyroid cancers have unique screening guidelines.

According to the American College of Physicians, if you have an average risk for breast cancer, you should:

  • talk to your doctor about whether you should start screenings before the age of 50 if you are between the ages of 40 and 49
  • get mammograms every other year from ages 50 to 74
  • discontinue mammograms when you reach the age of 75

The American Cancer Society recommends slightly different screening schedules for women with average risk for breast cancer. They recommend that women begin getting annual mammograms at age 45 with the option to switch to every other year at age 55.

If you’re at higher risk for breast cancer due to genetic or lifestyle factors, discuss your screening plan with your healthcare provider before age 40.

There are no formal guidelines for thyroid cancer screening. Healthcare providers typically recommend being evaluated if you have the following:

You should also consider getting your neck checked once or twice a year by your healthcare provider. They can detect any lumps and give you an ultrasound if you’re at increased risk for thyroid cancer.

There are unique symptoms for breast and thyroid cancers.

The most common symptom of breast cancer is a new mass or lump in the breast. The lump can be hard, painless, and have irregular edges.

It can also be rounded, soft, or painful. If you have a lump or mass on your breast, it’s important to get checked by a healthcare provider with experience diagnosing diseases in the breast area.

Sometimes breast cancer can spread and cause lumps or swelling under the arm or around the collarbone.

The most common symptom of thyroid cancer is also a lump that forms suddenly. It usually starts in the neck and grows quickly. Some other symptoms of breast and thyroid cancers include:

Breast cancer symptomsThyroid cancer symptoms
pain around the breast or nipple
nipples turning inward
irritation, swelling, or dimpling of breast skin
discharge from the nipple that isn’t breast milk
swelling and inflammation in part of the breast
thickening of nipple skin
chronic cough not caused by a cold or flu
difficulty breathing
difficulty swallowing
pain in the front part of the neck
pain going up to the ears
persistent hoarse voice

Talk to your healthcare provider if you’re experiencing any of these symptoms.

Treatment will depend on the type and severity of your cancer.

Breast cancer treatment

Local treatments or systemic therapies can treat breast cancer. Local treatments fight the tumor without affecting the rest of the body.

The most common local treatments include:

  • surgery
  • radiation therapy

Systemic therapies can reach cancer cells throughout the body.

These therapies include:

  • chemotherapy
  • hormone therapy
  • targeted therapy

Sometimes, healthcare providers will use hormonal therapy along with radiotherapy.

These therapies can be given at the same time, or hormonal therapy could be given after radiotherapy. Research suggests that both plans include radiation in order to lessen the formation of cancer growths.

Healthcare providers often detect breast cancer early, so more local therapies are used. This can lower the risk of exposing the thyroid and other cells to procedures that may increase the risk of cancer cell growth.

Thyroid cancer treatments

Treatments for thyroid cancer include:

  • surgical treatments
  • hormone treatments
  • radioactive iodine isotopes

Research suggests an association between breast cancer and thyroid cancer. More research is needed to better understand this association.

If you have breast cancer, talk to your healthcare provider about getting screened for thyroid cancer if you have symptoms. If you have thyroid cancer, ask your healthcare provider about getting breast cancer screening if you have symptoms.

Also talk with your healthcare provider about the possible connection between the two cancers. There may be something in your personal medical history that could increase your chances of thyroid or breast cancer.