Analysis of a large national database (the results of which were presented at the Endocrine Society’s 97th annual meeting, 5–8 March 2015, San Diego, CA, USA) has indicated that breast cancer survivors have an increased risk of developing thyroid cancer, particularly within 5 years of their breast cancer diagnosis.
“Recognition of this association between breast and thyroid cancer should prompt vigilant screening for thyroid cancer among breast cancer survivors,” commented lead investigator Jennifer Hong Kuo (Columbia University, NY, USA). Kuo advised that survivors of breast cancer should be counselled regarding their increased risk of thyroid cancer.
The study analyzed the National Cancer Institute’s Surveillance, Epidemiology, and End Results 9 database to identify the number of individuals diagnosed with breast and/or thyroid cancer between 1973 and 2011. In total, the investigators identified 704,402 individuals with breast cancer, 49,663 individuals with thyroid cancer and 1526 individuals who developed thyroid cancer after breast cancer.
On average, those who developed thyroid cancer after breast cancer received their breast cancer diagnosis younger than those who only developed breast cancer. Furthermore, these individuals were more likely to have been diagnosed with invasive ductal carcinoma, to have had a smaller focus of cancer and to have undergone radiation therapy as part of their breast cancer treatment. According to the Endocrine Society’s Hormone Health Network, radiation therapy to the head, neck or chest is a known risk factor for thyroid cancer.
Individuals who developed thyroid cancer after breast cancer were more likely to be diagnosed with a more aggressive type of thyroid cancer compared with those who had thyroid cancer with no prior breast cancer diagnosis; however, those with a prior breast cancer diagnosis developed smaller tumors and fewer patients required additional radioactive iodine treatment.
The study reports that those breast cancer survivors who developed thyroid cancer did so after a median of 5 years. Kuo therefore recommends that breast cancer survivors, especially those who received radiation therapy, should undergo a dedicated thyroid examination every year for the first 5 years after breast cancer diagnosis.
Kuo will next study the idea that tamoxifen treatment, which is usually given for 5 years following a breast cancer diagnosis, may play a role in increasing the risk of thyroid cancer. The incidence of thyroid cancer is increasing, and Kuo commented that researchers need a better understanding of the etiology behind this increase.