Breast Cancer Rates Drop with Less Hormone Replacement Therapy

A sharp decline in the rate of new breast cancer cases in 2003 and a sustained decrease in 2004 may be related to a national decline in the use of hormone replacement therapy (HRT), according to a new report.

Led by Dr. Donald Berry of the University of Texas M.D. Anderson Cancer Center and Dr. Kathy Cronin of NIH's National Cancer Institute (NCI), the research team used data from NCI's ongoing Surveillance, Epidemiology and End Results (SEER) program.

In the April 19, 2007, issue of the New England Journal of Medicine, the team showed that age-adjusted breast cancer incidence rates in U.S. women fell 6.7% in 2003. During the same period, prescriptions for HRT declined rapidly, following highly publicized reports from the Women's Health Initiative (WHI) study that showed an increased risk of breast cancer, heart disease, stroke, blood clots and urinary incontinence among postmenopausal women who were using hormone replacement therapy that included both estrogen and progestin.

The decrease in breast cancer incidence, the researchers found, began in mid-2002 and leveled off after 2003. From 2001 to 2004, the annual age-adjusted incidence of breast cancer dropped 8.6%. The decrease occurred only in women over the age of 50 and was more evident in women with cancers that were estrogen receptor (ER) positive—tumors that need estrogen in order to grow and multiply.

Understanding the relationship between cessation of HRT and breast cancer is difficult. Effects may vary depending on the type of HRT used and other factors specific to how the hormones affect the body. The researchers believe that withdrawing hormones may have slowed the growth of some small cancers and prevented their detection on mammograms. These cancers might eventually grow and be found later, leading to higher incidence rates in the future. Therefore, continued monitoring of both the pattern of breast cancer incidence and the use of HRT will need to be done.

Because this analysis is based on population statistics, the study doesn't prove a link between HRT and breast cancer incidence. Only a randomized clinical trial could prove causation. When the link between breast cancer and HRT was first confirmed in the WHI, which was a randomized clinical trial, women in the study were asked to discontinue their study medications (either placebo or hormones), and were encouraged to continue undergoing annual mammography. These women are still being followed, and the WHI researchers are expected to release a follow-up report later this year about the group who received estrogen and progestin HRT. Those results will likely provide a much higher level of evidence about the influence of HRT on breast cancer.

“The decision about use of HRT is complex,” says study researcher Dr. Christine Berg of NCI. “While HRT provides relief from the symptoms of menopause, it may also increase one's risk of breast cancer. It is important that women meet with their doctor to discuss what decision is right for them, particularly if they are at high risk for breast cancer.”