Hormones had been prescribed for decades in the belief that they helped ward off heart problems, dementia and a host of other ills beyond curing hot flashes. Many doctors and women, too, were reluctant to buy the new study's conclusions.
Now there is more evidence that hormones and breast cancer are linked.
A new analysis documents a staggering 7 percent drop in U.S. breast cancer rates in 2003. The report, presented Thursday at the San Antonio Breast Cancer Symposium, does not prove a link between hormone therapy and breast cancer, but strongly suggests it, many experts said.
"When I saw it, I couldn't believe it," statistician Donald Berry of the University of Texas M.D. Anderson Cancer Center in Houston said of the drop.
Cancers take years to form, so going off hormones would not instantly prevent new tumors. But tumors that had been developing might stop growing, shrink or disappear so they were no longer detected by mammograms, doctors theorized.
Cases dropped most among women 50 and older — the age group taking hormones. The decline was biggest for tumors whose growth is fueled by estrogen — the type most affected by hormone use.
The drop was seen in every single cancer registry that reports information to the federal government, and no big change occurred with any other major type of cancer. These are strong signs that the breast cancer decline is no statistical fluke or error.
"It's very difficult to wrap your arms around this subject of the various pros and cons of hormone replacement therapy," adds CBS News medical correspondent Dr. Jon LaPook.
About 200,000 cases of breast cancer had been expected in 2003; the drop means that about 14,000 fewer women actually were diagnosed with the disease.
Dr. LaPook explains more about hormone replacement Watch Alfonsi's report
"It's a big deal ... amazing, really," said another of the researchers, Dr. Rowan Chlebowski of Harbor-UCLA Medical Center in Los Angeles. "It's better than a cure" because these are cases that never occurred, he said.
About 200,000 cases of breast cancer had been expected that year; the drop means that about 14,000 fewer women actually were diagnosed with the disease.
A separate study by the American Cancer Society, currently in press with a medical journal, also documents the drop. Lead author Ahmedin Jemal attributes two-thirds of it to a decline in hormone use and the rest to mammography use leveling off, resulting in fewer tumors being detected.
"We are really trying to look at the big picture," he said. "You cannot rule out the effect of screening."
Breast cancer is the most common major cancer in American women and the second leading cause of cancer deaths in women. About 213,000 new cases are expected to occur in the United States this year and more than 1 million worldwide.