Risk of Thyroid Cancer Increases After Breast Cancer Diagnosis

Survivors of breast cancer more likely to develop aggressive form of thyroid cancer.

Breast cancer survivors carry an increased risk of developing thyroid cancer within 5 years of their initial breast cancer diagnosis, a recent study found.

Presented recently at the Endocrine Society's 97th annual meeting, the study indicates that survivors of breast cancer should receive counseling on the higher-than-average risk of developing thyroid cancer.

"Recognition of this association between breast and thyroid cancer should prompt vigilant screening for thyroid cancer among breast cancer survivors," lead investigator Jennifer Hong Kuo, MD, said in a press release.

Prior research on the connection between breast and thyroid cancer has been inconclusive in light of single-institution studies indicating a potential rise in thyroid cancer incidence following breast cancer.

The study analyzed the National Cancer Institute Surveillance, Epidemiology, and End Results 9 database to identify individuals diagnosed with breast and/or thyroid cancer between 1973 and 2011. Investigators found 704,402 patients with only breast cancer, 49,663 patients with only thyroid cancer, and 1526 patients with both diseases.

Patients diagnosed with both cancers were found to be younger on average when they were initially diagnosed with breast cancer compared with women diagnosed with breast cancer alone.

Patients diagnosed with both diseases were also more likely to have developed invasive ductal carcinoma, a smaller focus of cancer, and to have underwent radiation therapy as part of treatment for breast cancer. There was no observed difference in risk factors based on whether the cancer was hormone receptor positive or if it spread to the lymph nodes, according to the study.

Breast cancer survivors who developed thyroid cancer were more likely to develop a more aggressive type of thyroid cancer than patients who developed thyroid cancer alone. In these patients, the thyroid cancers were smaller, with fewer patients who required additional radioactive iodine treatment.

In light of thyroid cancer tending to occur at a younger age than breast cancer, survivors of breast cancer who subsequently developed thyroid cancer were on average 62 years of age, compared with patients who only developed thyroid cancer who were on average 45 years of age.

Researchers found that breast cancer survivors developed thyroid cancer at a median of 5 years. As a result, Dr. Kuo recommended that for the first 5 years following breast cancer diagnosis, patients should receive a dedicated thyroid exam, specifically survivors who received radiation therapy.

Additionally, researchers plan on evaluating whether treatment with tamoxifen, which is typically administered for 5 years after a breast cancer diagnosis, may play a role in the increased risk of developing thyroid cancer.