From MSNBC: Tamoxifen may not prevent cancer
Breast-cancer studies show no benefit; conclusions debated
By Linda Carroll
SPECIAL TO MSNBC
July 9 -Two European studies have failed to
confirm the finding that tamoxifen prevents
breast cancer. The new data appear to contradict
the results of the large multicenter American trial
that was halted earlier this year after researchers
discovered that women taking tamoxifen were
far less likely to develop breast cancer than
those treated with placebos.
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`I don't necessarily view
these studies as contradictory.'
- DR. BRUCE KRAMER
National Cancer Institute
IN THAT STUDY - part of the National Surgical
Adjuvant Breast and Bowel Project (NSABP) - new
breast cancers were reduced by nearly half among women
who took the drug, which is widely used to treat existing
breast cancer, for an average of three years.
But neither of the new studies, published in Friday's
issue of The Lancet, found that tamoxifen helped ward off
the disease.
"We have been unable to show any effect of tamoxifen
on breast-cancer incidence in healthy women, contrary to
the report from the NSABP-P1 study showing a 45 percent
reduction in healthy women given tamoxifen versus
placebo," reported Dr. Trevor Powles, lead author on one
of the new studies and a medical oncologist at the Royal
Marsden Hospital at Sutton in Surrey, England.
U.S. EXPERTS POINT TO DIFFERENCES
American cancer specialists disputed the apparent
discrepancy. "I don't necessarily view these studies as
contradictory," said Dr. Bruce Kramer, deputy director of
the division of cancer prevention at the National Cancer
Institute in Bethesda, Md. "That's because there are
differences in the design, differences in the populations of
women eligible for these three studies and differences in the
size of the studies."
For example, Powles' study of British women included
only 2,471 subjects - substantially fewer than the 13,000
women enrolled in the NSABP trial, Kramer explained. It's
possible that the British study would have found a protective
effect if it had been larger, he added.
With the large number of women enrolled in the
NSABP study, the chances that the results could be a
statistical fluke - the result of chance - are less than one
in 10,000, Kramer said.
In the British study, researchers followed women with a
family history of breast cancer for an average of about six
years. The ages of the women in the study ranged from 30
to 70. Of the women in the study, 1,238 received
tamoxifen, while 1,233 were treated only with placebos.
Ultimately, 34 of the tamoxifen-treated women developed
breast cancer, compared to 36 of those who received
placebos. The difference was not statistically significant.
In the second new study, Italian researchers led by Dr.
Umberto Veronesi followed 5,378 women, ages 35 to 70,
who had had a hysterectomy, in which the uterus is
surgically removed. The researchers chose to study women
who had undergone hysterectomies because one of the
possible side effects of taking tamoxifen is cancer of the
uterus. With the uterus removed, this is not a concern.
At the outset, none of the women in Veronesi's study
had an increased risk of developing breast cancer. In fact,
as the Italian researcher pointed out, women whose ovaries
have been removed in a hysterectomy have a lower than
average risk of developing the disease.
The women in the Italian study were followed for an
average of about four years, during which time nearly half
received tamoxifen, while the rest were treated with
placebos. At the end of the study, 19 of the
tamoxifen-treated women developed cancer, compared to
22 of the women treated with placebos. Again, the
difference was not regarded as significant.
"Tamoxifen was not significantly protective against
breast cancer in women at normal or slightly reduced risk of
the disease, at least in the duration of our follow-up,"
concluded Veronesi, a researcher at the European Institute
of Oncology in Milan.
But because the Italian study focused on low- to
average-risk women, the results of the study are not
comparable to the NSABP study, which looked only at
women whose risk of developing breast cancer was
four-fold higher than the average, said Dr. Victor Vogel,
director of the comprehensive Breast Program at the
University of Pittsburgh Cancer Institute and
McGee-Womens Hospital.
"You might conclude from this study that tamoxifen
doesn't work for low- or average-risk women," Vogel
added. "But you'd still have to be cautious. This just
suggests we need to have additional studies in low- and
average-risk women."
While the Italian study was larger than the British study,
it may have had an even smaller chance of proving that
tamoxifen could be beneficial, Vogel said. That's because
the Italian researchers were studying normal- and low-risk
women - a group that would develop few breast cancers.
There is another possible problem with both new
studies: the researchers allowed the women to take
hormone replacement therapy, Vogel said. "It's possible
that estrogen in combination with tamoxifen might negate the
protective effects of tamoxifen," he added.
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