A second report links hormone replacement therapy (HRT) with increased breast cancer risk in postmenopausal women. The new study findings suggest that the combination of progestin and estrogen heightens the breast cancer risk even more than estrogen therapy alone. Last week, a study published in The Journal of the American Medical Association found similar results.

Hormone replacement therapy with progestin-estrogen combinations grew rapidly in popularity in response to evidence that giving estrogen alone to menopausal women increased the risk of cancer of the endometrium (the lining of the uterus). Few studies have been conducted to examine the influence of combination therapy on the risk of breast cancer. Their study, which involved more than 3,500 women, did just that. Estrogen replacement therapy alone (ERT) increased the risk of breast cancer only in women who took estrogen for many years, the authors report, but the risk increased 6% for every 5 years of use.

Adding progestin to the HRT regimen, however, substantially increased the breast cancer risk, the results indicate. Five years of combination therapy increased a woman's risk of breast cancer by 24%, four times as much as ERT. The way in which the hormone combination was taken also affected the breast cancer risk, with estrogen and progestin taken sequentially during the month being slightly riskier than taking the estrogen and progestin together every day, the investigators found.

The increase in breast cancer risk associated with HRT did not seem to differ between women who currently used HRT and those who had stopped their HRT at least 2 years previously, the report indicates. This study provides the strongest evidence to date that progestins not only do not protect the breast from the (cancer-causing) effects of estrogen, but also increase substantially the small ERT-related increase in breast cancer.

Journal of the National Cancer Institute February 16, 2000;92.

Dr. Mercola's Comments:

If you haven't gotten it by now, it is important to wake up to the fact that synthetic progesterone (progestins like Provera) is not good for you. Unless you consider increasing your risk for breast cancer by 400 percent good. I find it most curious that the authors argue the benefits of estrogen-replacement therapy (ERT) in preventing heart disease outweigh the increased risk of breast cancer. You may have heard or seen some of the reports they calculated that for each (new) case of breast cancer in women due to long-term ERT use, more than six deaths from heart disease are prevented. I am not sure what calculator they used for this, because it is not true. The Journal of the American Medical Association (JAMA) has published many articles that show just as conclusively that it is a flawed fantasy promoted by the drug companies that estrogen protects against heart disease. The plain and simple truth is that it does not.