The rates of new breast cancer decline as soon as women quit hormone therapy, according to a report published online in Cancer Epidemiology, Biomarkers & Prevention. This supports the hypothesis that stopping hormones can lead to tumor regression.
In 2002, the Women’s Health Initiative published that breast cancer rates were higher in women taking estrogen and progestin than in those taking either a placebo or only estrogen. Since then, research has shown a rapid decline in new breast cancers, the use of hormone therapy, and in mammography screening.
Some have suggested that the reduction in hormone therapy use may have made tumors regress and thus caused the decline in the breast cancer rate, lead author Diana S.M. Buist, PhD, a senior investigator at Group Health Research Institute explained.
However, other theories suggest former hormone users are less concerned about breast cancer or see their doctors less often, and that they may receive mammography screening less often compared to women who have never taken hormones. “We set out to test this idea,” Buist said, “and our results seem to refute it.”
Researchers studied 741,681 woman-years of data (with a median of 3.3 years per woman) on 163,490 women aged 50 to 79 years who had no prior history of breast cancer.
“This is the first study to look over time at screening mammography use among individual women by their hormone therapy status linked with their breast cancer diagnoses,” Buist said.
Prior to 2002, former users of hormone therapy had lower rates of mammography screening compared with current users. However, Buist and colleagues found that this is no longer true. In fact, according to study results, former hormone therapy users had the same or even slightly higher mammography screening rates than current users.
“We concluded that differences in rates of screening mammography don’t explain the declines in rates of the incidence of invasive breast cancer among women who’ve stopped using hormone therapy,” Buist said.
Source: Group Health Research Institute.