Underactive Thyroid May Reduce Breast Cancer Risk

by Mary Shomon

April, 2003 -- Good news for female thyroid patients! A new study has found that having an underactive thyroid gland may reduce the risk of developing breast cancer. In addition, breast cancer may also grow more slowly in women with a history of hypothyroidism.

The research, conducted by the University of Texas-M.D. Anderson Cancer Center in Houston, looked at 1,100 women with newly diagnosed breast cancer, versus 1,100 healthy women.

Hypothyroidism occurred significantly more often in healthy women than in women with breast cancer. In fact, women with breast cancer were 57% less likely to have an underactive thyroid than healthy women.

Breast cancer was found in 80 participants who had a history of hypothyroidism, but it was generally less invasive breast cancer that had not metastasized to the lymph nodes, and was sensitive to estrogen. These women also tended to be older when first diagnosed with the disease.

According to lead researcher Massimo Cristofanilli, M.D., "These intriguing findings suggest a possible biological role of thyroid hormone in women with breast cancer that could offer some prognostic or therapeutic value, perhaps suggesting novel preventive strategies."

"Thyroid hormones and estrogen are both involved in regulating growth in a cell, including cancer cells, so if there is a dysfunction in the ability of a cell to use one hormone, it may potentially affect the capacity of growth regulation of the other," says Dr. Cristofanilli.

If results of a prospective trial, now being designed, bear out this conclusion, it may be possible to design a treatment that specifically and narrowly targets thyroid hormone receptors to help prevent breast cancer, according to Dr.

Source: Proceedings for the 2003 Annual Meeting of the American Association for Cancer Research.