April 20, 2010 (Washington, D.C.) -- There are two good drug options for preventing breast cancer in high-risk women, and more women need to take advantage of them, doctors say.
Updated results from a large breast cancer prevention trial confirm that both the old standby tamoxifen and the osteoporosis drug Evista can substantially cut the risk of developing breast cancer in high-risk postmenopausal women.
Tamoxifen works a little better, but Evista may be a little safer, says study head D. Lawrence Wickerham, MD, of Allegheny General Hospital in Pittsburgh.
But "only 5% to 20% of the tens of thousands of women" who could benefit from the drugs use them, says Gabriel Hortobagyi, MD, a breast cancer specialist at the University of Texas M.D. Anderson Cancer Center in Houston who was not involved with the work.
Over 192,000 women, about 150,000 of whom were postmenopausal, were diagnosed with breast cancer in 2009, he says.
Updated results from the STAR (Study of Tamoxifen and Raloxifene) trial were presented at the annual meeting of the American Association for Cancer Research and published online by the journal Cancer Prevention Research.
Tamoxifen has been used for years to help fight breast cancer's return. In 1998, the FDA approved tamoxifen for use by women who hadn't had breast cancer but were at high risk of developing the disease.
Evista, known generically as raloxifene, is taken by about half a million women in the U.S. to prevent and treat osteoporosis, or thinning of the bones. In 2007, the FDA approved it for breast cancer prevention in some high-risk postmenopausal women based on earlier results from STAR and other trials.
As a breast cancer preventive, they're recommended for women at higher-than-average risk because of genetic mutations, family history, or other factors, including age over 60.
Tamoxifen vs. Evista
The updated analysis of the federally funded study involved nearly 20,000 postmenopausal women followed for almost seven years during and after treatment with either tamoxifen or Evista.
Earlier findings from the study, published in 2006, showed that both drugs reduced the risk of breast cancer by about 50% in high-risk, postmenopausal women. But Evista appeared to carry fewer risks of side effects, with lower rates of uterine cancer and clotting problems.
The new findings suggest that several years after treatment, which lasts about five years, tamoxifen is substantially better than raloxifene at preventing breast cancer.
About two years after treatment ended, tamoxifen reduced the risk of invasive breast cancer by 50%, while Evista cut risks by 38%.
Put another way, Evista was 76% as effective as tamoxifen, says Wickerham, who serves as a consultant to makers of both drugs.
But women who took Evista "continued to have substantially fewer of the serious side effects, including uterine cancers, clotting problems, and cataracts, that seem to be barriers to tamoxifen use," he says.
There were 2.25 cases of uterine cancer per 1,000 women treated with tamoxifen vs. 1.23 per 1,000 among women treated with Evista. There were 3.30 blood clot events per 1,000 women treated with tamoxifen vs. 2.47 per 1,000 among women treated with Evista.
"The absolute risk of these problems for any given woman is quite low, regardless of treatment," says M.D. Anderson's Scott Lippman, MD.
There was no difference in death rates among the two groups. Neither of the drugs has been shown to extend lives in high-risk women.
Who Is Considered a High-Risk Patient?
So which drug is better for which women? Both drugs are only for women at high risk, doctors stress.
In the study, women were considered to be at high risk if their risk of developing breast cancer over the next five years was 1.67% based on a simple formula called the Gail model that takes into account age, family history, and other factors. By definition, anyone over age 60 was at high risk.
But Hortobagyi says he probably wouldn't give the drugs to a woman in her 60s who is otherwise healthy based on age alone. "It's a discussion each woman needs to have with her doctor. The more risk factors, the greater she will benefit."
If you and your doctor conclude you are at increased risk and you are not at risk for blood clots or uterine cancer, both drugs are good breast cancer prevention options, Hortobagyi says. If you are at risk for these problems, Evista is the better choice, he says.
All things being equal, some women may want to take tamoxifen because it is slightly more effective, the experts say.
On the other hand, postmenopausal women with thinning bones might want to consider Evista because it "offers two benefits in one," Lippman says.
The study only included postmenopausal women, but as a treatment for breast cancer, tamoxifen has a proven track record in premenopausal women as well, Hortobagyi says. Evista is only approved for use after menopause, so its safety and effectiveness in premenopausal women is unknown, he says.
High-risk premenopausal women who have had a hysterectomy -- and therefore a "close to nonexistent" risk of uterine cancer -- and who have no history of blood clots may want to talk to their doctor about taking tamoxifen, he says.
Both drugs cost about $140 a month or $8,400 for five years of treatment. In comparison, treating one case of early breast cancer can easily cost $50,000 to $120,000, according to Hortobagyi.