Updated May 21, 2013.

by Mary J. Shomon

September 2000 -- According to a retrospective study conducted at the University of Texas MD Anderson Cancer Center, younger women with thyroid cancer have an increased risk of developing breast cancer later in life. The study establishes a relationship between the post-surgical use of radioactive iodine (RAI) I31I treatments for thyroid cancer, and later development of breast cancer.


The authors of the study, "The Development of Breast Cancer in Women with Thyroid Cancer," are all from the The University of Texas MD Anderson Cancer Center Houston, TX. Their findings are being presented at the annual meeting of the American Academy of Otolaryngology--Head and Neck Surgery Foundation Annual Meeting in Washington, D.C.

Using the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database, the researchers found that young women (30-34 years) with thyroid cancer exhibited the greatest risk of developing breast cancer. Women who were between the ages of 40 and 44 at initial diagnosis of thyroid cancer were also at significantly elevated risk. The data suggested that the greatest risk appears 15-20 years after the thyroid cancer.

The study concluded that premenopausal adult Caucasian women who are treated for differentiated thyroid cancer are at increased risk to develop breast cancer five to 20 years later. Breast cancer, however, does not increase the risk of subsequent thyroid cancer.

This finding suggests that the increased risk of breast cancer after thyroid cancer is related to the thyroid cancer treatment. In particular, the RAI treatment is suspected to be the agent involved in increasing the cancer risk.

The authors' recommendation is for regular follow-up of all women patients with thyroid cancer and "judicious use of radioactive iodine as a treatment regimen."

What This Means for Thyroid Patients

It would seem prudent for women who have received RAI to pay particular attention to preventive factors for breast cancer, including diet, exercise, and healthy body weight. You should incorporate some form of regular screening - i.e., monthly breast self-exams, regular professional breast examinations, and/or mammograms - into your health care.

In my opinion, of critical importance to women who have had RAI treatment for Graves' Disease is the need for a definitive study looking at whether the lower levels of RAI used to ablate the thyroid also pose an increased risk of breast cancer. Given that RAI is the preferred treatment for hyperthyroidism in the U.S., this is an important question. It's already thought by some researchers that having an autoimmune thyroid disorder contributes to increased risk of breast cancer. But given that researchers are suggesting that the RAI is the factor that is the likely cause of the subsequent breast cancer in thyroid cancer patients, this question warrants further research.