Breast Cancer Survivors Have Increased Risk of Thyroid Cancer

Within 5 years of a breast cancer diagnosis, patients are at an increased risk of developing thyroid cancer, according to a new study, which was presented at the Endocrine Society’s 97th annual meeting in San Diego on March 5-8.

The study identified 704,402 patients with only breast cancer, 49,663 patients with only thyroid cancer, and 1526 patients who developed thyroid cancer after breast cancer. Women who developed thyroid cancer after their breast cancer diagnosis tended to be younger when their breast cancer was diagnosed when compared with women with breast cancer alone.

Breast cancer survivors who developed thyroid cancer were more likely to have a more aggressive type of thyroid cancer compared with patients who only had thyroid cancer, but their cancers were smaller in size.

“Recognition of this association between breast and thyroid cancer should prompt vigilant screening for thyroid cancer among breast cancer survivors,” said lead investigator Jennifer Hong Kuo, MD, assistant professor of surgery at Columbia University, New York City.

She recommended that breast cancer survivors receiving counseling about their risk of thyroid cancer. Next, Dr Kuo plans to study if tamoxifen treatment, which is typically given for 5 years after a breast cancer diagnosis, increases the risk of thyroid cancer.

This is not the first time an association between breast and thyroid cancers has been identified; however, the relationship has been controversial because prior studies were largely based on single-institution studies. The study presented at ENDO 2015 was based on an analysis of the National Cancer Institute’s Surveillance, Epidemiology, and End Results 9 (SEER 9) database, which includes data from 1973.

In 1984, a study using the Connecticut Tumor Registry identified an elevated risk of thyroid cancer following breast cancer. However, the study population consisted of just 1618 women with primary thyroid cancer and 39,194 women with primary breast cancer. The researchers determined that 34 thyroid cancer patients later developed breast cancer and 24 breast cancer patients later had thyroid cancer.