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NEW YORK, NY -- February 14, 2005 -- According to a new study, women
suffering from a common thyroid problem called hypothyroidism, a condition in
which the thyroid gland fails to produce enough thyroid hormone, are less likely
to develop breast cancer than women with normal thyroid function. The study,
published in the March 15, 2005 issue of CANCER (http://www.interscience.wiley.com/cancer-newsroom),
a peer-reviewed journal of the American Cancer Society, finds that a history of
hypothyroidism is associated with more aggressive forms of breast cancers,
suggesting that thyroid hormone may promote breast cancer biology.
Over a century ago physicians described using thyroid extract to treat breast
cancer. Later, studies found that one of the circulating thyroid hormones
actually sustained breast cancer cells, while animal studies found mammary gland
cells responded to thyroid hormones. Population studies have shown conflicting
patterns in the relationship between thyroid hormone and breast cancer. For
example, Japanese scientists found patients with thyroiditis - an elevated
thyroid hormone state - had a higher incidence of breast cancer, while other
scientists found high levels of thyroid hormones were protective against breast
cancer. Studies of benign thyroid disorders have also failed to demonstrate
associations between thyroid hormones and breast cancer biology.
To investigate and clarify the relationship between a history of hypothyroidism
and the risk of breast cancer, Massimo Cristofanilli, M.D. and colleagues at the
University of Texas M. D. Anderson Cancer Center in Houston compared the medical
records from 1136 women with breast cancer and 1088 healthy women attending
their breast screening clinic.
The researchers found women with primary hypothyroidism had a 61 percent lower
risk of developing invasive breast cancer. In addition, women with breast cancer
were 57 percent less likely to have hypothyroidism compared to healthy women.
Analysis of breast tumor pathology demonstrated that women with hypothyroidism
were diagnosed with earlier stage disease and smaller tumor size.
The authors say, "The observed association between hypothyroidism and breast
cancer may be due to the biologic effect of (the thyroid hormone) T3 at the
cellular level," adding that further studies of thyroid regulating hormones and
intracellular iodide concentrations may "indicate areas of intervention for
targeted preventive and therapeutic purposes."
SOURCE: John Wiley & Sons, Inc.