Numerous studies confirm that a woman’s greatest fear of hormone replacement therapy (HRT) is breast cancer.  Contrary to what many women believe, breast cancer as a cause of death ranks below other cancers, heart disease, stroke, and osteoporosis.

Statistical Risk

Many women are aware that the lifetime incidence of breast cancer is 1 in 8.  However, this statistic reflects a life-time risk.  When the risk is adjusted by age, it is quite different--1 in 77 in your forties, 1 in 42 in your fifties, and 1 in 45 in your eighties.

Until women reach their mid-fifties, death from breast cancer is greater than from heart disease.  After these years, heart disease deaths rise dramatically and breast cancer deaths decrease. The leading cause of cancer death in post-menopausal women is actually lung cancer.

Women may be justifiably fearful of breast cancer because everyone seems to know a woman who in the prime of her life has had breast cancer.  This fear must somehow be balanced with the facts of its relative risk.  But to put that fear in perspective, men die at a much earlier age than women but undoubtedly would give the same pause to a therapy that could be beneficial in increasing their life-span but that involved a slight increase in the relative risk of testicular cancer.

HRT and Breast Cancer

There are conflicting studies regarding the related risks of HRT to breast cancer.  The news media tends to report any study regardless of its size or significance.  Several years ago in the same week,  two studies about HRT were covered in the news that had opposite conclusions, confusing the issue even further.

When all of the major studies are looked at together in a meta-analysis, it appears that there is an approximate 20-30% increase in the relative risk of breast cancer for each 10 years of HRT use.  This means that a woman in her 60’s on HRT for 10 years would have a 1 in 29 risk instead of a 1 in 36 risk of developing breast cancer.

Recently, one study suggested that an estrogen/progesterone compound combination increased the risk even further.  It must be noted that this study used the estrogen Premarin in higher dosages than may now be recommended.  Also, the progesterone compound used was the synthetic medroxyprogesterone (Provera).  No study has examined whether micronized natural progesterone would prove to be any safer.

The results of the large scale Women's Health Initiative study (July 2002) confirmed some of the earlier studies showing a 24 per cent increase in the breast cancer rate for those taking the combination of Premarin (equine estrogen) and Provera (synthetic progestin) for longer than 5 years.  For those women who had a hysterectomy and were only taking Premarin, there was no increase in the breast cancer rate.  This most recent study has lead many to use micronized natural progesterone instead of Provera in those women who have a uterus.

HRT users who do develop breast cancer tend to get a less invasive and more treatable cancer, and some studies even show a lower death rate in HRT users.  It is not clear if this is due to the estrogen itself or due to the "healthy woman bias" producing an earlier detection--women taking HRT generally choose healthier lifestyles, dieting, exercising, not smoking, and having regular medical check-ups.

Other risk factors for breast cancer include:

Early menstruation, late menopause, and never having been pregnant have been shown to increase your risk for breast cancer.