14 Feb 2005
Discovery could lead to new direction for prevention, treatment research -
Researchers at The University of Texas M. D. Anderson Cancer Center have found
that women with a common thyroid gland disorder appear to have a reduced chance
of developing invasive breast cancer, according to a study published in the
March 15 issue of Cancer, out online Feb. 14.
In a retrospective case-control study of 2,226 females, researchers found that
women with primary hypothyroidism (under-active thyroid) had a 61 percent lower
risk of developing invasive breast cancer. Additionally, women newly diagnosed
with breast cancer were 57 percent less likely to have the under-active thyroid
gland condition compared to a control group of healthy women.
Even more, the breast cancer patients on the study who also had a history of
hypothyroidism tended to be older when diagnosed and have a less aggressive,
indolent variety of the disease that was sensitive to estrogen treatment.
"These intriguing and very exciting findings suggest a 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., associate professor in M. D. Anderson's Department of
Breast Medical Oncology and the study's lead author. "The study also draws
attention to the role of thyroid hormone and its potential interaction with
estrogen to promote the onset of breast cancer. We need to consider that while
in the past we've looked only at the role of estrogen on breast tissue to
promote the onset of cancer - thereby promoting research that brought
therapeutic and preventive hormonal approaches to the patient - many more
studies need to be done to explore the role of other hormones.
The influence of thyroid gland disease on breast cancer has been debated for
some time. Other smaller studies have focused on a population of women with
several thyroid conditions, such as hypothyroidism, hyperthyroidism (over-active
thyroid), thyroid cancer and others, and reported conflicting results on the
incidence of breast cancer. Consequentially, researchers were not sure what to
make of the different findings, Cristofanilli says.
M. D. Anderson's study is the first clinical investigation to examine the
characteristics of invasive breast cancer in patients with hypothyroidism and
compare the incidence of this common condition with a carefullyselected matched
control group. The study compared the medical records of 1,136 women treated at
M. D. Anderson for breast cancer to those of 1,088 healthy women who came to the
institution for breast cancer screening.
"Thyroid hormone and estrogen both share similar pathways in regulating
proliferation and growth in the target cells, including cancer cells. This well
known phenomenon of cross-talk between the receptor of these hormones may
promote or inhibit thereby determining the "fate" of a cell towards either a
regulated growth or a cancer," he says. "If results of a planned M. D. Anderson
prospective study bear out this conclusion, then it may be possible to design a
treatment that specifically and narrowly targets thyroid hormone receptors,
which might provide enough influence on the target cells to help prevent breast
cancer - perhaps even serving as a complement to tamoxifen," Cristofanilli says.
Even before this research is concluded, Cristofanilli believes that, as a first
step, all women diagnosed with breast cancer should have their thyroid function
tested to detect common disorders - namely hyper- or hypothyroidism - so that
women with both conditions can be closely monitored.
Nuclear receptors for thyroid hormone 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.
Source :
http://www.medicalnewstoday.com/medicalnews.php?newsid=20013