This
year, more than 178,000 women in the United States alone
will be diagnosed with breast cancer, and about 43,500 will
die of the disease. For many years, women at increased risk
for developing breast cancer had no proven means to reduce their
risk.
Women
had to rely on frequent checkups and periodic mammograms to
catch breast cancer at an early stage. Doctors sometimes suggest
that certain women at very high risk have preventive (prophylactic)
mastectomies, which is surgery to remove breast tissue before
cancer develops.
However,
the operation does not guarantee that breast cancer will be
avoided, because it is almost impossible to remove all the breast
tissue. Because tamoxifen is successful in reducing the incidence
of breast cancer, women at increased risk for developing
the disease now have another choice.
Tamoxifen
is a drug, taken in pill form, which has been used as a breast
cancer treatment for more than 20 years. Over the years Tamoxifen
not only prevented the original breast cancer from returning
but also helped to prevent the development of new cancers in
the opposite breast. Because of this it was believed that tamoxifen
might have a similar effect for healthy women at increased risk
of breast cancer.
The
breast cancer prevention trial,
BCPT, was a clinical trial designed to see whether tamoxifen,
a SERM, would prevent breast cancer in women who are
at an increased risk of developing the disease. Selective
estrogen receptor modulators SERMs
are drugs that have some estrogen-like properties and some anti-estrogen
properties.
For
example, tamoxifen acts against the effects of estrogen in breast
tissue, and it acts like estrogen in other body systems. Tamoxifen's
estrogen-like properties may slow or reduce bone loss, decreasing
bone fractures of the hip, wrist, and spine due to osteoporosis
in postmenopausal women.
Doctors
know that estrogen promotes the growth of breast cancer cells.
Tamoxifen's anti-estrogen activity may reduce the risk of breast
cancer by blocking the effects of estrogen on breast tissue
by slowing or stopping the growth cancer cells already present
in the body.
In
the BCPT, breast cancer was diagnosed half as often in the women
who were assigned to take tamoxifen compared with women who
did not take it. Women on tamoxifen also had fewer diagnoses
of noninvasive breast cancer, such as ductal carcinoma in situ.
Women
in the BCPT were randomized (selected by chance) to receive
either tamoxifen or a placebo (an inactive pill that looked
like tamoxifen). In a process known as "double blinding," neither
the participant nor her physician knew which pill she was receiving.
Setting up a study in this way allowed the researchers to clearly
see the true benefits and side effects of tamoxifen without
the influence of other factors.
Tamoxifen,
while clearly beneficial for breast cancer, is not without hazards.
Tamoxifen
prevented breast cancer and had no apparent serious side effects
for women ages 35 to 49, but in women over age 50 there was
an increased risk of serious side effects. Tamoxifen can increase
the risk of:
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