Drugs Prevent Breast Cancer -- for Some
Few Now Benefit; Safer Drugs Needed
There's been only one large study of Evista's ability to prevent breast cancer. It looked at a different group of women: 7,705 postmenopausal women with osteoporosis. In this group, Evista cut breast cancer risk by 76%. To prevent one case of breast cancer, 126 women would have to take Evista for 40 months.
Both tamoxifen and Evista have side effects. Both increase the risk of blood clots in the legs and lungs, Kinsinger says. But she's quick to point out that this risk is no greater than the risk of taking estrogen-containing hormone-replacement therapy. Unlike Evista, tamoxifen increases a woman's risk of uterine cancer. Each drug also has other annoying but less drastic side effects.
Which drug is better? Doctors are eagerly awaiting the results of the STAR trial, which is directly comparing the two drugs. Results are expected in 2006.
"One thing to keep in mind is that tamoxifen is FDA approved for breast cancer prevention but Evista is not. For now, we have to stick with tamoxifen because of that," Kinsinger says. "But Evista is a good example of a newer drug that has a better side-effect profile and a better effectiveness profile. So if it gets approved, we will have a better drug than tamoxifen."
Kinsinger hopes that newer, more effective, safer drugs than either tamoxifen or Evista will come along by the time the STAR trial finally shows whether Evista works better than tamoxifen.
"Clearly the STAR trial will help us understand which drug is better," she says. "But down the road we will have better drugs than either of these two."
Such drugs can't come too soon. Kinsinger says that in her own practice she tells many women about the benefits and risks of tamoxifen for breast-cancer prevention. Yet very few women decide to start taking the drug.
"Do you want to take a pill every day for five years and risk side effects if you are at higher risk of breast cancer but otherwise perfectly healthy? There are a lot of issues here we haven't explored yet," Kinsinger says. "I have not had many women interested. We don't yet have the drugs that would allow us to be more encouraging because of the concern about side effects. When we take a drug for treatment, we are willing to accept side effects. But when you apply this to healthy women -- most of whom are not going to get breast cancer -- we get more hung up on it."