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Despite promising studies on emerging drugs, tamoxifen
(brand name, Nolvadex) is still the best option for preventing a recurrence of breast cancer after surgery outside of a
clinical trial setting, according to a panel of experts assembled by the American Society
of Clinical Oncology (ASCO). The panel’s decision is based on an analysis of a
recently released study called ATAC (Arimidex and Tamoxifen Alone or in Combination),
which suggests that the drug Arimidex (generic
name, anastrozole) may be more effective than tamoxifen. Though the panel acknowledges the
potential of Arimidex and other similar drugs, they say there is not enough long-term
evidence to prove that tamoxifen is inferior. The panel cited a similar concern with the
drug raloxifene (brand name, Evista), which has shown promise in
clinical trials for preventing breast cancer in high risk women.
After the release of the ATAC study at the 24th annual San Antonio Breast Cancer
Symposium in December 2001, the American Society of Clinical Oncology put together
a panel of leading breast cancer experts to help women and physicians determine the value
of tamoxifen (a SERM) and another class of drugs called aromatase inhibitors. The ATAC
study, conducted by Dr. Michael Baum of the University College Hospital in London and his
colleagues, found that the aromatase inhibitor Arimidex was more effective than tamoxifen
at preventing a recurrence of breast cancer by 17%. After 30 months of treatment and 33
months of monitoring, the researchers found that 317 of 3,125 women who were given
Arimidex experienced a cancer recurrence compared to 379 of 3,116 women who were given
tamoxifen. Arimidex also worked better at preventing breast cancer in the opposite breast,
compared to tamoxifen. (The ASCO panel pointed out that the effect of Arimidex on a
patient’s survival has not been studied yet).
"While recent findings on the use of aromatase inhibitors for the prevention of
breast cancer recurrence are encouraging, data on long-term use of the drugs are needed
before a change in the standard of care is justified," said Eric Winer, MD, Director
of the Breast Oncology Center at the Dana-Farber Cancer Institute and chair of the panel,
in an ASCO statement. "Patients and physicians can rest assured that tamoxifen
remains the best option for use outside of clinical trials, and that it reduces the risk
of recurrence and improves overall survival with manageable side effects for most
women."
The panel did acknowledge possible benefits of aromatase inhibitors based on the ATAC
study, including a low occurrence of side effects. However, the experts say that the side
effects of tamoxifen are also generally low and that these efforts have been documented
over the past 25 years that tamoxifen has been used with breast cancer patients. Again,
more research is needed to study the long-term effects of aromatase inhibitors.
The panel recommends that aromatase inhibitors not be used outside of clinical trials.
In clinical trials, patients can be monitored closely by researchers and taken off
medication quickly if need be. Several recent clinical trials have shown the promise of
aromatase inhibitors. For example, in another study presented at the 2001 San Antonio
symposium, Matthew Ellis, MD, of Duke University Medical Center, and his colleagues
compared the effects of the aromatase inhibitor Femara
(generic name, letrozole) and tamoxifen in 324 post-menopausal women prior to breast
cancer surgery. Dr. Ellis and his team found that after four months of treatment, 60% of
women who were given Femara experienced shrinkage in the size of their cancer tumors
compared to 41% of women who were given tamoxifen. Moreover, taking Femara allowed tumors
to shrink enough in some women so they could avoid mastectomies
and have less invasive surgery instead (however, in most instances, Femara would be given
to women after surgery, not before surgery, as in the study). Femara also increased
patient survival time over tamoxifen in the study.
Despite the promising results of recent research, the American Society of Clinical
Oncology says that there is no firm evidence to suggest that women who have begun a
standard course of tamoxifen should consider switching to an aromatase inhibitor. However,
the panel did say that an aromatase inhibitor may be an option for women who have
experienced negative reactions to tamoxifen, if the physician approves.
The panel also acknowledged the potential of the drug raloxifene in helping to prevent
breast cancer in women at high risk for the disease. Raloxifene belongs to the same class
of drugs as tamoxifen (SERMS), and recent research has suggested that raloxifene is at
least equal to tamoxifen in preventing breast cancer in post-menopausal women over age 35.
However, the panel again said that long-term data are needed before raloxifene or any
other drug (besides tamoxifen) can be recommended as an additional option for women at
high breast cancer risk.
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