TUESDAY, July 24 (HealthDay News) -- Scientists have once again linked a drop in breast cancer rates from 2003 to 2004 to a parallel decrease in women's use of hormone therapy beginning in 2002.
The decline in breast cancer rates persisted even though mammography screening rates remained stable, said researchers at Kaiser Permanente, reporting in the August issue of the Journal of the National Cancer Institute.
"The message is pretty straightforward," said study lead author Dr. Andrew Glass, senior investigator at the Kaiser Permanente Center for Health Research in Portland, Ore. "If you need to take hormone therapy to block menopausal symptoms, do it for the shortest duration and the lowest dose."
"We now have a second observation that when we discontinue or decrease hormone therapy, we have a very significant drop in breast cancer incidence," added Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "This is another piece of information that I think women should use in determining whether or not they want to take hormone therapy. To me, it shows that combination therapy [estrogen plus progestin] does increase the incidence of breast cancer. Women need to take this into consideration."
Last December, a different set of researchers reported a precipitous drop in the incidence of breast cancer in 2003 and suggested that the downward trend was the result of millions of women discontinuing use of hormone replacement therapy.
The decline in the number of U.S. women taking hormone replacement therapy came after publication of the results of the landmark Women's Health Initiative (WHI) trial in 2002. That study, involving 16,608 participants, was halted after researchers found elevated health risks among HRT users, most notably for breast cancer and stroke.
Since then, a debate has continued over the utility and safety of hormone therapy, with health officials advising women to take HRT only when needed and for as short a period as possible.
The authors of the new study reviewed the medical histories of 7,386 women diagnosed with invasive breast cancer and treated at Kaiser Permanente Northwest between 1980 and 2006. The records were available through Kaiser Permanente's computerized database, which includes a tumor registry and clinical, pathology, radiology and pharmacy data systems.
From the early 1980s to the early 1990s, breast cancer rates rose 26 percent, then an additional 15 percent through 2001. From 2003 to 2006, rates dropped by 18 percent.
The 26 percent increase paralleled increases in the rates of mammograms as well as increases in the use of hormone therapy, especially combination therapy, the researchers said.
The 15 percent increase -- from 1992 to 2002 -- echoed a continued rise in the use of hormone therapy, although mammogram rates remained stable from 1991 rates.
The drop in breast cancer rates starting in 2003 coincided with a 75 percent drop in hormone therapy rates, although mammography rates remained the same.