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Analysis of Million Women Study Flawed, Link Between Hormone Replacement Therapy and Breast Cancer Remains

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Many research studies have shown a link between increased breast cancer risk and hormone replacement therapy (HRT) to treat bothersome menopausal symptoms. The Million Women Study was one of the largest of these studies. A group of experts reviewed the study and concluded that it wasn't done properly.

The new evaluation of the Million Women Study was published online on Jan. 16, 2012 in the Journal of Family Planning and Reproductive Healthcare.

While the results of all the studies on HRT and breast cancer risk aren't exactly the same, there is good evidence that:

  • HRT increases the risk of being diagnosed with invasive breast cancer.
  • Breast cancer risk increases in the first several years of using HRT; risk appears to increase the longer a woman uses HRT.
  • Combination HRT (containing both estrogen and progesterone) increases breast cancer risk more than estrogen-only HRT.
  • High-dose HRT increases risk more than low-dose HRT.

The Million Women Study included nearly 1.3 million women in the United Kingdom and was designed to find links between diet and lifestyle factors and health problems such as cancer. The women enrolled in the study between 1996 and 2001. More than half (55%) of the women had used some form of HRT at some time in their lives and 35% were using HRT when the study results were first reported. The study reported that 15,759 breast cancers were diagnosed in the 1.3 million women. All of the links between HRT and breast cancer outlined above were confirmed by the first report on the Million Women Study results.

Recently, experts reviewed how information in the Million Women Study was obtained, recorded, and analyzed. Based on the review, the experts concluded that some of the conclusions made from the original Million Women Study analysis aren't reliable because of problems with the way the information was analyzed. Still, experts are confident that the links between using HRT and breast cancer risk are still very real, based on the results of many other studies.

Menopausal side effects can dramatically reduce quality of life for some women. These women have to weigh the benefits of HRT against the risks. If you're having severe hot flashes or other menopausal side effects and are considering HRT, talk to your doctor about all of your options. Ask how you can minimize your breast cancer risk AND relieve your symptoms. Be sure to discuss the pros and cons of different types of HRT.

Some evidence suggests that the breast cancer risk associated with HRT will be lower if you can wait to use HRT until 5 years after menopause starts. If you do decide to take HRT, ask if you can take an estrogen-only, low-dose formula and try to take it for the shortest time possible. You also may want to ask about vaginal or transdermal HRT.

Learn more about more about menopause and ways to manage side effects on the Breastcancer.org Managing Menopausal Symptoms pages.

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