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Nurses' Health Study links Estrogen use to Breast Cancer

May 10th 2006

Nurses' Health Study links Estrogen use to Breast Cancer

HRT Effects

The Nurses' Health Study (NHS) is an ongoing longterm cohort study examining the health of nurses compared to the general population. It is an observational study that, while interesting, falls short of the precision of a randomized clinical trial. The study, nevertheless, is important because it has prompted further research.

In the NHS, HRT use (either estrogen alone or estrogen/progestin) has been examined among these women for its potential effects on disease outcomes. As many know, it found lower rates of heart disease among hormone users and higher rates of breast cancer.

While these findings are informative, they haven't been paralleled (COMPLETELY) in clinical trials. For example, NHS found that women who initiated HRT at ANY AGE reduced their risk of heart disease.


But the Women's Health Initiative (WHI) found no such benefit - combined hormones upped the risks for heart disease, blood clots, and strokes throughout it's 5.2 year duration and estrogen alone, after 7 years, increased the risk of stroke and blood clots, though the latter finding wasn't as pronounced as it was for Prempro. (Heart attacks were SLIGHTLY but significantly higher in years 1 and 2 but the risk dissipated over the course of the trial.) While some experts chose to discredit the WHI e-alone heart findings by overhyping an insignificant decrease in heart attacks for women in their 50s, this primary prevention trial certainly discredited the validity of most observational data, including NHS, and put a huge dent in scientific thinking. But that's not the whole picture. Comment on this Article at our Forum

When looking at the NHS, we see that the WHI did confirm the long suspected link between hormone therapy and breast cancer, but the findings between the 2 studies haven't totally matched up. WHI found that combined therapy (Prempro) caused a significant spike in breast cancer risk after only 4 years, which precipitated that arm's early termination.


Estrogen alone (Premarin) did not find a higher risk OVERALL after 7 years and there was actually a nonsignificant reduction in breast cancer. While the North American Menopause Society and Wyeth, the maker of Premarin, gobbled this up and professed that estrogen alone PREVENTED breast cancer, new findings from NHS, though not definitive, have added yet another wrinkle to this story - it too found an insignificant DECREASE in breast cancer for <10 years of estrogen use, but the risk started to climb in years 10-14 and after 15 years, the risk was significantly higher. Again, it's not real proof that estrogen causes breast cancer, but it does confirm the current findings of WHI, which lasted only 7 years.

While I personally believe estrogen alone couldn't possibly reduce breast cancer risk (since it defies basic biology) and probably increases the risk EVENTUALLY after many years of use, by the same token, I don't think it would be responsible to run with the results of an observational study and overlook the only clinical trial we have. After all, that's what contrarians on the other end of the stick have been doing, lending credibility to the heart findings of NHS and ignoring the proven stroke, memory and (early) heart risks seen in WHI.


An observational study, like a laboratory experiment, does NOT COUNT AS PROOF. It is suggestive, nothing more! After all if NHS were truly definitive, it would have matched up completely on all accounts with the WHI. But since its heart findings failed to be replicated, its data on breast cancer needs to be looked at cautiously as well. It may be real, but again, it may not.  

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Jonathan Raymond

Books on Cancer

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Important:  The material on Best Syndication is for informational purposes only and is not a substitute for medical advice or treatment for any medical conditions. You should promptly seek professional medical care if you have any concern about your health, and you should always consult your physician before starting a fitness program.

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Copyright 2005 Best Syndication                   Last Updated Saturday, July 10, 2010 09:46 PM