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Senior Citizen Health & Medicine
Tamoxifen Only Benefits Women at Very High Risk of
Breast Cancer
Very small
likelihood it'll reduce mortality at lower end of high-risk range
July 24, 2006 - Most women at "high risk" for
breast cancer do not increase their life expectancy by taking the drug
tamoxifen, according to a new study funded by the National Cancer
Institute. These women, the only ones eligible to take tamoxifen, have
been diagnosed with a minimum 1.67 percent risk of cancer over five
years. These researchers suggest it takes risk greater than 3%,
particularly in women who have not had a hysterectomy, to see potential
benefit from tamoxifen.
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In addition, the research shows that tamoxifen is
an extraordinarily expensive cancer-prevention strategy, costing as much
as $1.3 million per year of each life saved.
The study by researchers from UC Davis, UCSF, the
University of Pittsburgh and McMaster University in Ontario, Canada will
be published in the Sept. 1 issue of the American Cancer Society's
journal Cancer, and appears online on today.
"We found that for women at the lower end of the
high-risk range for developing breast cancer, there is a very small
likelihood that taking tamoxifen will reduce mortality," said Joy
Melnikow, professor of family and community medicine at UC Davis School
of Medicine and Medical Center and lead author of the study.
"This would support revising the current
recommended risk threshold for physicians to counsel women about
tamoxifen."
Tamoxifen was approved by the U.S. Food and Drug
Administration in 1998 for breast cancer prevention in women who have at
least a 1.67-percent chance of developing the disease over the next five
years. Such women are considered at high risk for breast cancer.
Groups such as the U.S. Preventive Services Task
Force and the Canadian Task Force on Preventive Health Care recommend
that physicians counsel women above this threshold about the benefits
and risks of tamoxifen as a means of preventing the disease.
Tamoxifen is a selective estrogen
receptor-modulating drug used to treat estrogen receptor-positive breast
cancers. The landmark chemoprevention study for tamoxifen found that
among women who meet the minimum FDA eligibility criteria for "high
risk" (i.e., a 5-year risk of breast cancer of at least 1.67%) tamoxifen
use resulted in a 49 percent reduction in (ER positive) breast cancers.
Its effect on survival has not been studied before.
However, tamoxifen is associated with significant
adverse effects, including cataracts requiring surgery, deep vein
thromboses, endometrial cancer and stroke. Women taking tamoxifen, if
they do develop breast cancer, are also more likely to develop an
estrogen receptor-negative tumor, which has a worse prognosis. (Cancers
prevented by tamoxifen are mostly estrogen receptor-positive).
In the new study, Melnikow and her colleagues
calculate that tamoxifen can be expected to extend life expectancy only
when a woman's five-year risk of developing breast cancer reaches 3
percent or more.
In particular, life expectancy benefit was seen for
women who already had a hysterectomy, and thereby eliminated the drug's
risk of endometrial cancer.
When taking into account ER-negative breast
cancers, an approach that has not been investigated before, mortality
rates actually increased slightly until 5-year risk reached more than 2
percent.
Cost-effectiveness was also calculated in the
study. For women at the 1.67-percent risk level, taking tamoxifen to
stave off breast cancer came to $1.3 million per year of life saved
based on the U.S. price of the drug -- a prohibitively expensive
cancer-prevention strategy.
Melnikow and her co-authors note, however, that the
cost-effectiveness equation could be improved if pharmaceutical prices
were negotiated at a national level. At Canadian prices, for example,
the researchers showed that taking tamoxifen to prevent breast cancer
comes to $123,780 per year of life saved for women at the 1.67-percent
risk level.
In comparison, annual flu shots cost about $980 per
year of life saved for patients ages 65 and older; colonoscopy every 10
years costs about $11,000 per year of life saved for people 50 and
older; and annual mammography costs about $58,000 per year of life saved
for women ages 40 to 80.
To arrive at their findings, Melnikow and her
colleagues used a complex mathematical model based on a hypothetical
group of 50-year-old women.
Melnikow specializes in research to better
understand women's health-care preferences and how women make
health-care decisions. In a study published in the journal Cancer last
year, she reported that among women with a five-year breast cancer risk
of 1.67 percent or higher, fewer than one in five were inclined to take
tamoxifen to prevent the disease. Concern about potential side effects
was the primary reason.
Note: UC Davis Cancer Center is the nation's 61st
National Cancer Institute-designated center, serving a region of more
than 6 million people in inland Northern California.
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