New Clues on Breast Cancer Decline
Increases and Drops in Breast Cancer Rates Tied to HRT Use
July 24, 2007 -- New research shows a dramatic drop in breast cancers in
2003 and 2004, while offering some of the best evidence yet that a parallel
drop in the use of hormone replacement therapy (HRT) was responsible for the
The findings make it clear that since 1990, breast cancer rates have been
moving in tandem with hormone therapy use, researcher Andrew G. Glass, MD, of
Kaiser Permanente Northwest tells WebMD.
The declines were confined to estrogen-receptor positive (ER+) breast
cancers, which are sensitive to the same hormones used in menopausal hormone
The study appears in the Aug. 1 issue of the Journal of the National
“This was strong biologic evidence that the cancer decline was related to
hormone use,” he says.
Breast Cancer, HRT, and Mammography
Using Kaiser Permanente’s extensive patient database, Glass and colleagues
were able to review 26 years' worth of health information on 7,386 breast
They also compared breast cancer incidence rates among health system members
with mammography usage and hormone therapy use between 1980 and 2006.
Among women aged 45 and older, breast cancer rates rose by 25% from the
early 1980s to the early 1990s and continued to rise at a slower rate (15%)
Breast cancer rates among health plan members dropped by 18% between 2003
Other key findings from the study:
- The 25% rise in breast cancers during the 1980s corresponded with sharp
increases in both mammography screening and HRT usage during the
- The 15% rise in breast cancers from 1992 to 2002 corresponded with a
leveling off of mammography usage and a continued increase in the use of
menopausal hormone therapy.
- The dramatic drop in breast cancers starting in 2003 paralleled a
precipitous drop in HRT usage following the 2002 release of a widely reported
government study questioning the safety of menopausal hormone therapy.
Mammography screening rates did not change during the period.
Does HRT Cause Breast Cancer?
But if breast cancers take years and even decades to develop, as experts
say, why would the sharp decline in HRT use in one year be reflected in a
dramatic drop in breast cancers the next?
One theory is that menopausal hormone therapy fuels the progression of
already existing precancerous cells within the breast, just as antiestrogen
treatments like tamoxifen slow the growth of existing ER+ tumors.
“We have known that these cancers respond to hormones used for treatment,”
Glass says. “What we didn’t know was that the use of hormones for other reasons
may encourage the growth of these cancers.
So does menopausal hormone therapy actually cause breast cancers or just
promote their growth?
The answer isn’t clear, but University of Texas M.D. Anderson Cancer Center
professor of biostatistics Donald A Berry, PhD, says the latter scenario is