Breast cancer drop linked to hormone therapy decline
The malignancy rate is not caused by a reduction in mammography use, as scientists had speculated, new research concludes.
By Thomas H. Maugh II
Times Staff Writer
July 25, 2007
Patient treatment records from a large HMO show that the recent decline
in breast cancer rates is linked to a sharp drop in use of hormone
replacement therapy and not to reductions in the percentage of women
getting mammograms, as many scientists had speculated, researchers said
Dr. Andrew G. Glass and his colleagues at Kaiser Permanente Northwest
in Portland, Ore., found a drop in breast cancer rates among their
patients from 2003 to 2006 even though mammography rates remained
virtually constant, they reported in the Journal of the National Cancer
A lowered mammography rate results in fewer breast
cancers detected. Researchers are not sure why the rate declined, but
contributing factors include the closing of some mammography centers,
the cost, the discomfort and fewer visits to doctors' offices because
of the drop in hormone replacement therapy.
By using a patient
population for whom the mammography rate remained constant, "we were
able to disentangle mammography from hormones," Glass said.
an editorial in the same journal, Dr. Donald A. Berry and Dr. Peter M.
Ravdin of the University of Texas M.D. Anderson Cancer Center in
Houston agreed that a reduction in mammography use could not be
responsible for the bulk of the decline in breast cancer.
only known factor that would seem to explain the precipitous drop in
incidence is the sharp decrease in use of menopausal hormone therapy,"
No one is suggesting that estrogen triggers the
formation of breast tumors. Rather, most researchers think it
accelerates growth of existing tumors. Stopping hormone replacement
therapy slows the growth of small tumors, delaying their detection for
perhaps a couple of years and producing an apparent decline in
incidence, Berry and Ravdin speculated.
estrogen and progestin fell by nearly half in 2003 after 2002 results
from the Women's Health Initiative, a National Institutes of Health
program, linked an increased breast cancer risk to hormone replacement
Nearly 40% of post-menopausal women had used the
hormones to ease menopausal symptoms, such as hot flashes, and to
prevent conditions related to aging, including osteoporosis.
Ravdin and their colleagues reported last year that breast cancer rates
fell 7% in 2003, attributing the decline to decreased use of hormone
therapy. A report this year showed that by the end of 2004, the
incidence had dropped 11.8% among women over 50, the primary recipients
of hormone therapy.
But an analysis earlier this year by
epidemiologist Ahmedin Jemal and his colleagues at the American Cancer
Society concluded that the decline in breast cancer had begun in 1999
and that a significant fraction of the decrease could be attributed to
a 4% drop in mammography rates over the period in question.
wrote that Kaiser's figures on mammography differed from national
figures and questioned Glass' conclusion that the drop in hormone usage
was the most important factor in the breast cancer rate decline. "All
you can say is that their data is suggestive," he said.
and his colleagues reviewed the histories of 7,386 women diagnosed with
invasive breast cancer and treated at Kaiser Permanente Northwest from
1980 through 2006.
They concluded that breast cancer rates rose
26% from the early 1980s to the early 1990s, rose an additional 15% to
2002 , then dropped 18% from 2003 through 2006.
The initial rise
occurred in concert with sharp increases in mammography rates and the
rise of hormone replacement therapy. During that period, the use of
mammography grew from just a few percent of patients to about 75% of
all older women.
The 15% increase in breast cancer rates from
1992 to 2002 paralleled a continued rise in hormone replacement
therapy, while mammography rates remained at the 1991 level.
sharp drop in breast cancer rates starting in 2003 occurred in concert
with a 75% drop in hormone use among the Kaiser patients, while
mammography rates remained at 1991 levels. By the end of 2006, they
found, the breast cancer rate — 126.2 cases per 100,000 women — was the
lowest since the mid-1980s.
The bulk of the change over the
years was in the so-called estrogen-receptor-positive tumors, whose
growth is stimulated by estrogen. These tumors account for 70% to 80%
of all breast cancers.
The Kaiser data showed that the
estrogen-receptor-negative tumors did not experience the increase seen
for the receptor-positive tumors during the 1980s and 1990s. They did,
however, drop sharply from 2003 to 2006, for reasons that are unclear.
Pines, president of the International Menopause Society, noted,
however, that Glass' data showed a decline in breast cancer beginning
in 1999 similar to that of Jemal's data. "There must be another,
non-hormonal and still unknown factor explaining, at least in part,
these changes in incidence."
Long-term therapy may be
associated with a small increase in risk, but "in women younger than
60, hormone therapy," particularly estrogen alone, he concluded, "is
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