Based on a retrospective analysis, researchers at Columbia University Medical Center reported an increased incidence of thyroid cancer among patients with breast cancer. The results were presented during the session “Thyroid/HPT Axis-Clinical/Translational” of the Endocrine Society’s 97th annual meeting in San Diego, March 5-8, 2015, entitled “Increased Incidence of Thyroid Cancer Among Breast Cancer Survivors: An Analysis of the SEER 9-Database.”
Previous studies had already suggested a relationship between breast and thyroid cancers. In this new study, researchers analyzed a database (SEER-9) with 499,402 breast cancer patients and 53,853 thyroid cancer patients from 1990-2011. They found that the incidence of thyroid cancer among breast cancer patients was higher in comparison to the general population. Normally, thyroid cancer developed in patients at a median of five years after breast cancer. They also found that those patients who developed thyroid cancer after surviving breast cancer had a more aggressive type of disease compared to thyroid only cancer patients.
The study recommended systematic annual thyroid exam after a breast cancer diagnosis, especially for those who underwent radiotherapy. This type of treatment is highly effective for destroying breast cancer cells but it may also affect normal tissue, which in part explains the associated increase in thyroid cancer. The Endocrine Society’s Hormone Health Network notes that radiation therapy to the head, neck or chest is a known risk factor for thyroid cancer.
The incidence of thyroid cancer is increasing, and this study suggests an association between the two types of cancer, contributing to an improved understanding of the etiology for such an increase. “Recognition of this association between breast and thyroid cancer should prompt vigilant screening for thyroid cancer among breast cancer survivors,” observed study’s lead investigator Dr. Jennifer Hong Kuo.
Besides radiotherapy, tamoxifen (a blocker of estrogen’s effects) is a typical treatment for breast cancer and is also regularly prescribed for prevention in high risk-cases. Whether tamoxifen plays a role in an increased risk of developing thyroid cancer still requires further studies.