Breast cancer rate decline tied to less hormone use

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 declines in mammography, researchers said Tuesday.

Dr. Andrew 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 Institute.

A lower mammography rate means fewer breast cancers are 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.

In an editorial in the same journal, Dr. Donald Berry and Dr. Peter Ravdin of the University of Texas M.D. Anderson Cancer Center in Houston agreed that declines in mammography could not be responsible for the bulk of the decline in breast cancer.

"The only known factor that would seem to explain the precipitous drop in incidence is the sharp decrease in use of menopausal hormone therapy," they wrote.

No one is suggesting that estrogen triggers the formation of breast tumors. Rather, most researchers think that it accelerates the 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.

Prescriptions for estrogen and progestin fell by nearly half in 2003 after 2002 results from the Women's Health Initiative linked an increased breast cancer risk to hormone replacement therapy.

Berry and Ravdin reported last year that breast cancer rates fell 7 percent in 2003, attributing the decline to decreased use of hormone therapy. A second report this year showed that by the end of 2004, the incidence had dropped 11.8 percent among women over 50, the primary consumers of hormones.




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