The incidence of breast cancer in the United States dropped precipitously in 2003, and new research suggests the downward trend was the result of millions of women discontinuing use of hormone replacement therapy.
The drop was most pronounced among women over 50, and was seen mostly with estrogen receptor-positive breast cancers, which are fueled by the hormone estrogen. As many as 14,000 fewer women were diagnosed with breast cancer in 2003 than in 2002, the researchers stated.
“This is big news,” said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System, in Baton Rouge. “This has profound public health implications for women in this country.”
The decline in the number of women taking HRT came just 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 raged about the utility and safety of HRT, with health officials advising women to take HRT only when needed and for as short a period as possible.
The authors of the current study looked at data on women in nine regions across the country from 1990 to the end of 2003.
Between 1990 and 1998, the incidence of breast cancer incidence in the United States increased at 1.7 percent per year. Between 1998 and 2003, incidence began to go down at 1 percent per year and, in 2003, there was a 7 percent drop in a single year.
According to the study authors, who presented their findings Thursday at the annual San Antonio Breast Cancer Symposium, this was the largest single drop ever in breast cancer incidence within a single year. “Something went right,” study author Dr. Peter Ravdin, a research professor in biostatistics at M.D. Anderson Cancer Center in Houston, said in a statement.
Further analyses revealed that the decline was most evident in patients older than 50 and for estrogen receptor-positive tumors. The steepest decline (12 percent) was in women aged 50 to 69 who had estrogen receptor-positive tumors. Women in that age range with estrogen receptor-negative tumors saw a 4 percent decline in incidence.
Women with estrogen receptor-positive breast cancer showed an 8 percent decline vs. 4 percent for women estrogen receptor-negative breast cancer.
The incidence of breast cancer in the United States had been increasing for the two decades prior to July 2002, and experts had speculated that HRT may have played a role.
According to the researchers, about 30 percent of women over the age of 50 had been taking HRT in the first part of this decade and about half of those stopped using HRT in late 2002. Estrogen receptor-positive tumors will stop growing if the fuel they need is cut off, which may explain the suddenness of the decline.
Still, it’s not certain that HRT caused the decline, only that the association is a strong one and further studies need to be done, the researchers stated.