SAN ANTONIO -- Significantly fewer American women were diagnosed with breast cancer in 2003, and a drastic drop in the use of hormone therapy is the most likely reason, researchers reported yesterday.
Breast cancer diagnoses dropped by 7 percent overall and by about 15 percent in women over 50, the group most likely to have been taking hormone therapy before a well-publicized federal warning scared millions into stopping in 2002.
It won't be certain that the decreases are not an aberration until April, when figures for 2004 are released. Indeed, researchers from the National Cancer Institute and other agencies reported the 2003 decline in September but played down the significance, saying they couldn't be sure the trend was real. Before this, the number of breast cancer cases had risen steadily for two decades and then leveled off.
But a University of Texas researcher, Dr. Peter Ravdin, and his colleagues didn't think the drop was a random occurrence, noting that the 7 percent decline was not only steep, but also consistent across all nine regional cancer registries maintained by the cancer institute. The drop means 14,000 fewer women were diagnosed with the disease.
Yesterday, Ravdin created a buzz among the 8,000 international experts at the annual San Antonio Breast Cancer Symposium when he presented the team's conclusions. While conceding that "we don't have 100 percent proof that it's hormonal therapy," the data were "pretty convincing," said Ravdin, of the M.D. Anderson Cancer Center.
Other researchers agreed. "These are very exciting data," said Dr. Dennis Slamon of the University of California, Los Angeles, who is not associated with Ravdin's work. "I think he's onto something that's real."
Dr. Nazanin Khakpour, a surgical oncologist and director of breast surgery at the University of Maryland Greenebaum Cancer Center, said that hormone therapy most likely is not causing cancer but is fueling the growth of tiny pre-existing tumors.
Shutting off the hormone supply may slow or halt the growth of tumors, keeping them below the threshold of detection.
But Khakpour cautioned that this is just a one-year snapshot - too short to draw firm conclusions. Women taking hormones or contemplating taking them, she says, shouldn't make any drastic decisions without first consulting their doctors.
Some experts, however, are convinced that the link between hormones and a decline in breast cancer cases is real enough.
"It all fits with what we know about the biology of breast cancer," said Dr. Patricia Ganz, a breast oncologist at UCLA's Jonsson Cancer Center.
"This is pretty powerful information," Ganz said of the study. She said that she would advise any of her patients on hormone replacement therapy to consider the consequences of continuing therapy.
Dr. Ahmedin Jemal, a cancer occurrence researcher at the American Cancer Society, said he recently found a similar result in his research - an overall drop of about 6 percent, compared to the Texas researchers' finding of a 7.2 percent drop. His study is set to be published in the journal Cancer Epidemiology Biomarkers & Prevention. "It's really promising," he said. "But you can't make a trend based on one year's data. If it happens the next year and the year after, it probably means a lot." He said the theory linking the drop in cancer rates to hormone pills also needed further vetting.
He added that it will probably take researchers two or three more years to determine whether the drop in cancer rates was due to women stopping hormone treatments.
According to Ravdin's team, the drop in hormone use among women is the only reasonable explanation for the change in breast cancer incidence.
First, the cancer decline was found to be most pronounced in women over 50, the age group where hormone use is concentrated. The drop also occurred entirely in hormone-sensitive breast cancers. Tumors whose growth is unrelated to hormone activity were diagnosed at the same rate as in previous years.
More than 200,000 U.S. women are diagnosed with invasive breast cancer every year, and the majority of these tumors are fueled by steroid hormones, mainly estrogen and progesterone.
The only other event that might have caused such a significant drop in breast cancer diagnoses, Ravdin said, is the decrease in mammography screening that followed a 2002 report questioning the benefit of mammograms for healthy women.
But the overall drop in mammography use between 2000 and 2003 was only 1 percent. Even for women ages 50 to 64, the drop was only 3 percent.
Referring to the fact that the cancer decrease occurred so soon after the drop in hormone use, Ravdin said the effect of hormones in the breast is probably not to initiate tumors - which can take years to develop - but to promote the growth of existing cancers too small to be detected.