Letrozole, a drug that derails the body’s production of estrogen, reduces breast cancer recurrences in women who have exhausted the usefulness of the anticancer drug tamoxifen, a new drug trial has revealed.
Tamoxifen stops breast cancers in many women by interfering with estrogen’s proliferative effect on tumor cells. But taking tamoxifen for more than 5 years provides no additional benefit, compared with going off the drug after that period.
Researchers identified 5,157 post-menopausal women who had taken tamoxifen for about 5 years and randomly assigned them to take either an inert pill or letrozole, which wipes out nearly all estrogen in the body.
The scientists stopped the study when it became clear that the group receiving letrozole had roughly three-fifths as many breast cancer recurrences as did women getting the placebo, says study coauthor Paul E. Goss, a medical oncologist at Princess Margaret Hospital in Toronto. Researchers then offered letrozole to all participants, each of whom had been followed for 2.4 years on average. The report appears in the Nov. 6 New England Journal of Medicine.
Letrozole disables an enzyme called aromatase, which the body needs to make estrogen. Another aromatase inhibitor, the drug anastrozole, is also being tested for cancer-fighting abilities (SN: 11/24/01, p. 327: Enzyme fighter works as well as tamoxifen).
Although tamoxifen’s anticancer effect levels out at 5 years, there’s no question that the drug imparts a residual benefit even after long-term users stop taking it. Indeed, no one knows how long the benefits of tamoxifen or the aromatase inhibitors might linger. That and the question of whether the drugs might interact in good or bad ways when given simultaneously are the topics of several studies now under way.
Letrozole is marketed as Femara by Novartis in New York, which was a sponsor of the newly reported trial.
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