Breast cancer rates drop when women quit hormone therapy, study shows

The number of breast cancer cases in the United States dropped markedly after women quit combination hormones for postmenopausal symptoms in droves in the early part of this decade, according to a paper published today in The New England Journal of Medicine.

Investigators also found that taking estrogen plus progestin for five years doubled a women's chances of developing breast cancer — the most detailed indication yet that the cancer risks may rise in tandem with the duration of hormone therapy.

The findings, based on an analysis of the landmark Women's Health Initiative study, further strengthens the suspected causal link between hormone therapy and breast cancer, the paper's authors said.

Researchers halted the federal Women's Health Initiative study three years early, in July 2002, after concluding that women who were randomly assigned to take Prempro, an estrogen-progestin pill, faced heighted risk of breast cancer as well as heart attack, stroke and blood clots.

The announcement stunned physicians, who for two decades had routinely prescribed hormones for postmenopausal women in the belief that they protected against heart disease and brittle bones.

Hormone prescriptions around the nation fell precipitiously, from 60 million in 2001 to 20 million in 2005. That corresponded with a steep decline in breast cancer cases among women enrolled in the Prempro clinical trial, said Ross Prentice,a biostatistician at the Fred Hutchinson Cancer Research Center and one of the paper's coauthors.

Within a year of the women quitting Prempro, breast cancer diagnoses among them fell by 28 percent, to 1 in 231, compared to 1 in 166 for women who had stayed on the hormones for five years.

The rapidness of that reversal was unexpected, Prentice said. Within a year of qutting hormones, a woman's risk of breast cancer subsided to near the 1 in 217 rate for women who'd taken Prempro for less than three years.

The number of breast cancer cases in the United States have dropped by about 20,000 each year following warnings about combination hormones. The latest analysis "suggests that could be due to the remarkable cessation hormone therapy," Prentice said.

Crude estimates, Prentice said, show that 12,000 of the 20,000 fewer breast cancer cases may be attributable to the decline in Prempro use.

Dr. Rowan Chlebowski,the study's lead author and a chief investigator at Los Angeles Biomedical Research Institute, said the findings bolster, if not definitively prove, the causal link between combination hormone therapy and some breast cancers.

Chlebowski acknowledged that some physicians remain skeptical about the connection. Still, he said evidence is strong enough to warrant second thoughts by doctors and patients about continuing hormone therapy beyond three to five years.

Kyung Song: 206-464-2423 or ksong@seattletimes.com