Breast Cancer: Arimidex vs. Tamoxifen
Study Shows Arimidex Beats Tamoxifen for Prevention of Cancer Recurrence
Dec. 14, 2007 (San Antonio) -- Even after treatment ends, Arimidex beats out
tamoxifen in preventing breast cancer recurrence in women with hormone-fueled
Updated results from this landmark trial also show that the increased risk
of fractures associated with Arimidex therapy disappears after treatment
In the study, more than 5,000 women with hormone-receptor-positive tumors
were followed for more than three years after treatment was stopped. The
researchers show that an additional 25% of recurrences were prevented by
Arimidex, compared with tamoxifen, says John F. Forbes, MD, professor of
surgery at the University of Newcastle in Australia.
During treatment, nearly 3% of women taking Arimidex had bone fractures vs.
only 2% on tamoxifen. More than three years after treatment ended, the
percentage was about 1.5% in both groups.
Forbes reported the findings here at the annual San Antonio Breast Cancer
Symposium. Results of the study, which was funded by AstraZeneca, maker of
Arimidex, were simultaneously published online in the journal Lancet
Studies have shown that Arimidex is better at preventing relapses than
tamoxifen during the five years that women are being treated with these
What we didn't know, Forbes says, is what would happen after women stop
"The news here is that the hoped-for carryover effect seems to be
true," William Gradishar, MD, a breast cancer specialist at Northwestern
University in Chicago, tells WebMD.
"The safety issue, particularly with regard to bone disease, is
reassuring as well," says Gradishar, who was not involved with the
Arimidex and other aromatase inhibitors shut down the body's ability to make
Tamoxifen blocks estrogen's effects, but not in the same way as Arimidex and
its sister drugs Femara and Aromasin. Tamoxifen blocks estrogen from getting
into cancer cells, slowing tumor growth.
Arimidex Cuts Breast Cancer Relapses
The landmark study involved postmenopausal women with early-stage breast
cancer. They were given either tamoxifen or Arimidex for five years, following
breast cancer surgery.
The new analysis followed only about 5,000 of these women who had
hormone-receptor-positive tumors. These are the tumors that are targeted by the
aromatase inhibitors such as Arimidex.
More than eight years after treatment started -- and more than three years
after it stopped -- Arimidex scored better than tamoxifen on almost every
- It lowered the risk of breast cancer relapse by 15% compared to
- It reduced the spread of cancer to other parts of the body, such as
the lungs or liver by 16% compared to tamoxifen
- It slashed the chances of a tumor in the other breast by 40% compared
At five years, 2.8% fewer women on Arimidex had their cancer recur compared
with those on tamoxifen; at nine years, the figure was 4.8%.
But doctors still can't say that Arimidex saves lives. Similar numbers of
women in both groups died.
Forbes tells WebMD that's probably because the women are aging -- their
average age is now 72 -- so many of them are dying of causes other than breast
"We should be focused on preventing recurrences. If a woman doesn't have
breast cancer, she won't die from it," he says.
In developing countries, about 75% of all breast cancers occur in
postmenopausal women; of those, about 80% are fueled by hormones.