One year after millions of post-menopausal women in the United States stopped using Hormone Replacement Therapy (HRT) in 2002, the number of new breast cancer cases dropped by 7% nationwide. Researchers from The University of Texas M. D. Anderson Cancer Center believe the two are linked – that the incidence of breast cancer went down largely because so many older women stopped using HRT.

The investigators are reporting their findings at the 29th annual San Antonio Breast Cancer Symposium.

The researchers found that:

— There was an overall 7% fall in breast cancer incidence in 2003, compared to 2002
— There was a 12% fall in breast cancer incidence among women aged 50-69 in 2003, compared to 2002, specifically those diagnosed with estrogen receptor positive (ER-positive) breast cancer
— 14,000 fewer women were diagnosed with breast cancer in 2003, compared to 2002

Researcher Peter Ravdin, M.D., Ph.D., said “It is the largest single drop in breast cancer incidence within a single year I am aware of. Something went right in 2003, and it seems that it was the decrease in the use of hormone therapy, but from the data we used we can only indirectly infer that is the case. But if it is true, the tumor growth effect of stopping use of HRT is very dramatic over a short period of time, making the difference between whether a tumor is detected on a mammogram in 2003 or not.”

Lead researcher, Donald Perry, Ph.D., said he and his team were surprised at how big the drop was and how soon it happened. He said “Incidence of breast cancer had been increasing in the 20 or so years prior to July 2002, and this increase was over and above the known role of screening mammography. HRT had been proposed as a possible factor, although the magnitude of any HRT effect was not known. Now the possibility that the effect is much greater than originally thought all along is plausible, and that is a remarkable finding.”

A large study of 16,608 women, the Women’s Health Initiative study, was abruptly stopped in July 2002 when it was found that older women using HRT (estrogen and progestin combination) had a significantly higher risk of developing invasive breast cancer. About one third of women over 50 in the USA had been taking HRT before the study.

Ravdin said “Research has shown that ER-positive tumors will stop growing if they are deprived of the hormones, so it is possible that a significant decrease in breast cancer can be seen if so many women stopped using HRT.”

Perry said “It takes breast cancer a long time to develop, but here we are primarily talking about existing cancers that are fueled by hormones and that slow or stop their growing when a source of fuel is cut. These existing cancers are then more likely to make it under mammography’s radar.”

The researchers have cautioned that as their study is based purely on population statistics, they cannot be completely sure why the numbers have dropped.

The National Cancer Institute and M.D. Anderson funded the study.

http://www.mdanderson.org