Hypothyroidism associated with reduced breast cancer

April 07, 2003

TORONTO - Women with a common thyroid gland disorder appear to have a reduced chance of developing invasive breast cancer, say researchers at The University of Texas M. D. Anderson Cancer Center.

In a retrospective case-control study of 2,226 females, researchers found that women newly diagnosed with breast cancer were 57 percent less likely to have an under-active thyroid gland, a condition called hypothyroidism, compared to a control group of healthy women.

Of further note, researchers say that the breast cancer found in 80 participants who had a history of hypothyroidism was of a less aggressive, indolent variety that was sensitive to estrogen. Also, these women were generally older when first diagnosed with the disease.

"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," says Massimo Cristofanilli, M.D., an assistant professor in the Department of Breast Medical Oncology. The results of the study were published in the Proceedings for the 2003 Annual Meeting of the American Association for Cancer Research.

The influence of thyroid gland disease on breast cancer has been debated for some time, but this is the first study to examine the characteristics of invasive breast cancer in patients with hypothyroidism and compare the incidence of this common condition with a carefully selected matched control group, Cristofanilli says. Other smaller studies have focused on a population of women with several thyroid conditions (such as hypothyroidism, hyperthyroidism, thyroid cancer and others) and reported controversial results on the incidence of breast cancer. "Consequentially, researchers were not sure what to make of the different findings," he says.

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

Nuclear receptors for thyroid hormones and estrogen are part of the "superfamily" of receptors that contribute to control cell growth and differentiation. Hormones must bind to this family of important proteins to exert their functions, and depending on the hormone to which they bind, can either stimulate or inhibit the growth of cells, Cristofanilli says.

Estrogen controls growth of female reproductive tissues, such as is found in the breasts, and thyroid hormones control energy metabolism in tissue.

Hypothyroidism - a condition estimated to affect approximately 20 percent of older women - is produced when the thyroid gland, located in the front of the neck, fails to produce enough thyroid hormone. Insufficient levels of specific types of thyroid hormone may affect all body functions, and can slow patient functioning, causing mental and physical sluggishness.
Contact: Laura Sussman or Julie Penne, 713-792-0655

University of Texas M. D. Anderson Cancer Center

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