Blog | Wednesday, May 4, 2011

About the Premarin study and breast cancer


This week a paper came out in JAMA showing a surprising reduction in breast cancer cases among women who had hysterectomies and then took Premarin, an estrogen-only remedy compounded from steroids in horses' urine.

Costa Rican Saddle Horse, graphite pencil drawing by Arsdelicata via Wikimedia CommonsThe research merits attention because it's part of the Women's Health Initiative and is well-done by several measures: The study is large, placebo-controlled and randomized. The investigators followed 10,739 post-menopausal women ages 50 to 79, all who previously had surgical removal of the uterus. The women took CEE (conjugated equine estrogens) at a dose of 0.625 mg by mouth per day, or a placebo. The trial was stopped a year early, after an average follow-up of seven years, after the analysts noted that more women taking Premarin had strokes. But I digress ...

The main findings were two: 1) Premarin, at the dose prescribed, had no clear effect on cardiovascular disease, overall, either way; and 2) there was a significant reduction in invasive breast cancer among women taking estrogen in this study. More precisely: the incidence of breast cancer was 0.27% in women who took Premarin and 0.35% in the placebo group. For the stats-guys: the relative risk was 0.77, with 95% confidence intervals of 0.62 to 0.95.

The findings were covered by major news organizations and other women's health bloggers. Still you may wonder, what's Medical Leson's take on this subject?

According to the New York Times as many as a third of women in the U.S. have had hysterectomies. The Centers for Disease Control says that approximately 600,000 hysterectomies are performed each year in the U.S. No matter what the numbers, which seem to me discordant, my first reaction is to wonder why so many women have their uterus removed.

About the apparently lower incidence of breast cancer, it may be that this particular dose of estrogen in the form of Premarin does tend to reduce or somehow suppress breast cancer in post-menopausal women who've had hysterectomies.

But it could just as well be a statistical fluke.

If you examine a sufficient number of outcomes in a research group of thousands of women, you're likely to find one aberration or another. What we do know is that most breast cancer cells do express receptors for estrogen, which can stimulate those cells' growth.

Presumably, time and the scientific process will yield the truth about Premarin and other hormones some people take so that they might feel better. Then again ...

Personally, I wouldn't go near the stuff.

This post originally appeared at Medical Lessons, written by Elaine Schattner, ACP Member, a nonpracticing hematologist and oncologist who teaches at Weill Cornell Medical College, where she is a Clinical Associate Professor of Medicine. She shares her ideas on education, ethics in medicine, health care news and culture. Her views on medicine are informed by her past experiences in caring for patients, as a researcher in cancer immunology and as a patient who's had breast cancer.