Scientists have 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 the US researchers, reporting in the August [2007] 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, Oregon. "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, chairperson of haematology/oncology at Ochsner Health System in Baton Rouge, Los Angeles.

"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 [oestrogen plus progestin] does increase the incidence of breast cancer. Women need to take this into consideration."

 Last December [2006], a different set of researchers reported a steep drop in the incidence of breast cancer in 2003, and suggested the downward trend was the result of millions of women discontinuing use of hormone replacement therapy (HRT).

The decline in the number of US women taking HRT 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 7386 women diagnosed with invasive breast cancer and treated at Kaiser Permanente Northwest between 1980 and 2006. The records were available through Kaiser Permanente's computerised database, which includes a tumour registry and clinical, pathology, radiology and pharmacy data systems.

From the early 1980s to the early 1990s, breast cancer rates rose 26 per cent, then an additional 15 per cent through 2001. From 2003 to 2006, rates dropped by 18 per cent.

The 26 per cent 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 per cent 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 per cent drop in hormone therapy rates, although mammography rates remained the same.

"When HRT went down, breast cancer rates went down and mammography rates remained the same," Glass said. "This was an important finding, because others had suggested maybe the drop in breast cancer rates was because mammograms had gone down, but it didn't happen in the Kaiser numbers. The only thing we can figure out is, it's probably related to HRT, that fluctuations in HRT are the most likely explanation for fluctuations in breast cancer rates."

The increase in breast cancer rates occurred primarily in women over the age of 45 who had oestrogen receptor-positive breast cancer.

According to Glass, this study is the first to document all these different factors - mammography, hormone therapy, breast cancer and oestrogen-receptor status - in one study.

But one expert found the study's conclusions lacking. "This is an interesting look at the picture but really is not evidence-based medicine," said Dr Lila Nachtigall, director of the women's wellness programme at New York University Medical Center and professor of obstetrics and gynaecology at New York University School of Medicine.

The study did not correlate individual cases of breast cancer with hormone use, therefore issues of causality cannot be decided, she added. "To try to prove causality is confusing to doctors and patients," she said. "I think it's a combination of things."

More health research news

Originally posted August 2007

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