Nurses' Health Study
links Estrogen use to Breast Cancer
May 10th 2006
|
 |
|
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.
Jonathan Raymond
Correspondent
Books on Cancer
Keywords and misspellings: prostrate hormane
treetments brane braine canser cancar abc world news tonigh prosetate
ransel
|
RSS Feeds to Cancer News
