TUESDAY, Aug. 14, 2007 (HealthDay News) -- A decline in women's use of hormone therapy, not any drop in mammography-linked detection, is likely responsible for the recent U.S. drop in breast cancers, says new research.
"Ours is the only study that has looked at a purely screened population. I think our study definitely says that that it's not because of screening," said lead researcher Dr. Karla Kerlikowske, professor of medicine and of epidemiology and biostatistics at the University of California, San Francisco, and director of the Women Veterans Comprehensive Health Center, part of the VA San Francisco.
"With the data that we have, hormones are the most logical explanation," said Kerlikowske, whose team published its findings online Aug. 14 in the Journal of the National Cancer Institute.
"This is pretty profound," added Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "Women have to make decisions in their lives, and the drugs [hormones] have not been taken off market. Women have to understand there is an associated risk of developing breast cancer when taking combined estrogen and progestin," he said.
The UCSF study follows closely on the heels of several others that have tried to explain a sharp decline in breast cancer incidence in 2003 to 2004.
The drop coincided with a rapid decline in postmenopausal hormone therapy starting in 2002, when the results of the Women's Health Initiative (WHI) were released. The WHI was halted early after researchers found elevated health risks, including breast cancer, among women taking the combined formulation of estrogen plus progestin.
Some have suggested that a decline in screening mammography was responsible, but other studies, including one published in July in JNCI, also found hormone therapy to be the likely culprit.
Kerlikowske and her colleagues looked at data on more than 600,000 mammograms performed between 1997 and 2003 on women aged 50 to 69.
In this group of women, use of hormone therapy declined by 7 percent a year between 2000 and 2002, then by 34 percent annually between 2002 and 2003.
Over the same period of time, breast cancer rates declined annually by 5 percent and estrogen-receptor-positive breast cancer rates fell by 13 percent annually from 2001 to 2003, a significant association.
The message for women?
"Women should hopefully take hormone therapy for as short a time as possible for [menopausal] symptoms," Kerlikowske said.
There is also some reassurance in the fact that breast cancer risk goes down when hormone therapy is discontinued, she added, although more data on this phenomenon is needed.
Convincing some women to curtail the use of HRT might be difficult, however.
"The problem is, we've grown so used in the last 40 or 50 years to having women take hormones that it's hard to break that paradigm shift," Brooks said. "A lot of women and a lot of doctors think that if I take hormones, I'm going to stay youthful, and that's a hard thing to break. But the data is the data."
There's more on the Women's Health Initiative at the U.S. National Institutes of Health.