A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology (April 2009)
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Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.

What is the study about?
There appears to be a link between breast cancer, hypothyroidism and thyroid cancer. This may be due to the radiation treatments for breast cancer. This study looked at how many patients treated for breast cancer also developed hypothyroidism. It also looked at whether having radiation therapy as a treatment for breast cancer increased a patient’s risk for developing hypothyroidism.

The full article title: Reinertsen KV, Cvancarova M, Wist E, Bjoro T, Dahl AA, Danielsen T, Fossa SD. thyroid function in women after multimodal treatment for breast cancer stage II/III: comparison with controls from a population sample. Int J Radiat Oncol Biol Phys 2009.

What was the aim of the study?
This study was done to examine if hypothyroidism was more common in women with breast cancer treated with surgery, radiation therapy and chemotherapy as compared to women in general. The study also looked at the effects of radiation treatment on becoming hypothyroid.

Who was studied?
Women in Norway with stage II/III breast cancer treated with surgery, radiation and chemotherapy from 1998-2002 were studies. These women were under 75 years old. Women of similar age from a general health survey in Norway without breast cancer made of the general population.

How was the study done?
A total of 861 women were asked to complete a questionnaire and give blood to measure thyroid levels in their blood and a total of 403 women agreed to participate. The women were asked if they had a thyroid problem and, if so, were they diagnosed before or after they were treated for breast cancer?

What were the results of the study?
Almost 1 in 4 women with breast cancer reported having a thyroid problem as compared to 1 in 10 in the general population. Hypothyroidism was the most common thyroid problem in these women and two out of three hypothyroid women were diagnosed with their hypothyroidism after being treated for breast cancer. There was a slight increase in hypothyroidism in patients treated with radiation therapy.

How does this compare with other studies?
Other large studies have found that the risk of hypothyroidism is not increased in patients who received radiation therapy. However, overall more breast cancer patients were found to have hypothyroidism than cancer-free patients.

What are the implications of this study?
This study suggests that women with breast cancer should have thyroid tests checked and be evaluated for hypothyroidism periodically after their treatment.

— Heather Hofflich, MD



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