University of Chicago researchers who reviewed 37 published studies found breast cancer survivors were 1.55 times more likely to develop thyroid cancer than women who hadn’t had breast cancer. And, female thyroid cancer survivors were 1.18 times more likely to get breast cancer than women who hadn’t had thyroid cancer, researchers said.
“This is a real risk,” said study lead author Dr. Raymon Grogan, director of the university’s endocrine surgery research program.
Thyroid cancer cases have nearly tripled in the United States over the past 30 years, and breast cancer is the most common cancer among women, according to background notes with the study. Thanks to medical advances, more women are surviving each cancer, Grogan said.
The report was published Feb. 5 in the journal Cancer Epidemiology, Biomarkers and Prevention.
Nineteen of the studies analyzed breast cancer patients and their risk of thyroid cancer. Another 18 looked at thyroid cancer cases and their incidence of breast cancer. The researchers then combined the data and calculated the odds of a women having thyroid cancer after breast cancer and vice versa.
In addition, the researchers combed through the studies to find reasons why these cancers seemed related. One explanation was that women who survive either cancer were more likely to be screened and examined so that other cancers were found early.
Another possible connection was that breast cancer and thyroid cancers share hormonal risk factors. There is some evidence that exposure to estrogens and to thyroid-stimulating hormones may contribute to both cancers, Grogan said.
A third theory points to radiation therapy, which has been shown to increase the risk for lung, esophageal and blood cancers, and sarcomas. Also, earlier research found that radioactive iodine, used to treat thyroid cancer, may play a small role in the development of other cancers, including breast cancer, but that is not clear, Grogan said.
I think the first explanation is without merit, in fact just reverse the order on the theories. The most probable cause of increased risk for a second cancer is the treatment for the first cancer, especially radiation therapy.
Hormonal factors also play a role. Unfortunately, when a woman develops estrogen dominant breast cancer conventional medicine just looks at using the estrogen pathway to deliver chemotherapy. No one questions why estrogen is out of balance and what can be done to correct the very thing that caused the cancer in the first place.
A simple urine test can determine if estrogen metabolites are out of kilter and represent an increased risk of cancer. However, the test is seldom run.
TSH (Thyroid Stimulating Hormone) has a normal range of 0.4 to 4.5 mU/mL. However, the American Board of Endocrinology recommends a healthy range of 1 to 2 mU/mL. Women with slightly underactive thyroid function run high normal TSH level for years, increasing their risk of cancer. This occurs both with and without thyroid medication.
The Bottom Line:
Women should have their TSH measured as part of their yearly physical exam. A baseline urine estrogen metabolite panel should also be run and repeated until the levels are normal. Women who have a history of either cancer should be even more vigilant.
Source: February 5, 2016 National Institutes of Health