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Bone Drug Cuts Risk of Breast Cancer: Study: Osteoporosis Medicine Has Fewer Side Effects Than Tamoxifen

Posted on: Tuesday, 18 April 2006, 00:00 CDT

By Emily Ramshaw, The Dallas Morning News

Apr. 18--The bone-strengthening drug raloxifene can prevent invasive breast cancer just as well as better-known tamoxifen, with fewer serious side effects, one of the largest-ever clinical breast cancer trials has found.

For years, health care providers have championed the benefits of prescribing tamoxifen to post-menopausal women at high risk of developing breast cancer. But the drug's side effects -- from blood clots to cataracts to uterine cancer -- have scared many women away.

The study of tamoxifen and raloxifene, sponsored by the National Cancer Institute and coordinated by cancer researchers across the nation, shows that the osteoporosis drug raloxifene is equally effective at preventing invasive, or noncontained, breast cancer and has fewer side effects. Experts estimate 500,000 post-menopausal women are taking raloxifene to treat or prevent osteoporosis.

"This allows post-menopausal women another option, one that may even be more acceptable, and not seen as a cancer drug," said Dr. Michael Grant, a breast surgeon at Baylor University Medical Center at Dallas. "There's still a place for tamoxifen. But doctors will feel more comfortable writing [a prescription] for raloxifene than for tamoxifen."

The study randomly assigned tamoxifen (Nolvadex) and raloxifene (Evista) to nearly 20,000 post-menopausal women older than 35 at high risk for breast cancer. Baylor was the seventh-largest enrollment site in the nation, with 285 women. UT Southwestern Medical Center at Dallas and Harris Methodist Fort Worth Hospital also participated in the study, which lasted four to five years.

Both drugs reduced invasive breast cancer instances by about 50 percent: 167 women on raloxifene got breast cancer, compared with 163 in the tamoxifen group.

What this means is that for every 1,000 women at high risk for breast cancer who are prescribed either drug, 17 will be diagnosed with the disease within four years. If the 1,000 women aren't prescribed medication, 34 of them will be diagnosed with breast cancer in the same time period. Experts say 150,000 post-menopausal women will learn they have breast cancer each year.

The average age of the study participants was 58, and about 93 percent of them were white. More than 70 percent of the women had a mother, a sister or a daughter with a history of breast cancer.

How it works

Tamoxifen and raloxifene work the same way: They're from a family of drugs that block the growth of tumor cells that feed off estrogen. And they share side effects, from the common -- such as hot flashes -- to the rare: blood clots and stroke.

But tamoxifen's side effects tend to be more severe, researchers say. And the drug has also been linked to a heightened risk of uterine cancer, a major deterrent for some women. Raloxifene has "virtually no increase in uterine cancer," said Dr. Leslie Ford, associate director for clinical research in the National Cancer Institute's Division of Cancer Prevention.

According to the study, more than half of the participants had had a hysterectomy and were not at risk of uterine cancer. Of those with a uterus who took tamoxifen, 36 developed uterine cancer, compared with 23 women on raloxifene -- a major statistical difference, researchers say.

The prevalence of blood clots and cataracts was lower in women taking raloxifene. And tamoxifen users reported more hot flashes, more night sweats and more menopausal symptoms than those on raloxifene.

But participants had equal levels of heart attacks, stroke and bone fractures. In all, close to 200 women died during the study -- about half on each of the medications.

Pros vs. cons

Researchers also indicated that raloxifene is not as effective as tamoxifen at preventing non-invasive breast cancer -- less-deadly cancers that have not spread throughout the breast.

While this finding was surprising, said Dr. David Euhus, medical director of the clinical research office at UT Southwestern, raloxifene will still "knock tamoxifen off the shelf." It has fewer side effects, it doesn't have the "cancer" stigma, and to top it off, it's cheaper, he said. Generic tamoxifen costs about $100 a month, experts say. Raloxifene costs $75 a month.

But other experts say this study won't lead to a phaseout of tamoxifen.

Although raloxifene is on the market for prevention and treatment of osteoporosis, it still isn't FDA-approved for breast cancer prevention. And it hasn't been linked to preventing cancer in pre-menopausal women; tamoxifen has.

In a study of 13,000 pre- and post-menopausal women at high risk for breast cancer published in 1998, researchers determined that tamoxifen reduced the risk of breast cancer by 50 percent. In the placebo group, 175 women got invasive breast cancer. There were 89 cases among the women taking tamoxifen.

But researchers in that study voiced concerns that tamoxifen might increase the risk of uterine cancer, and they hoped to find a drug that would be similarly effective with fewer side effects.

The new study of tamoxifen and raloxifene "is good news for women. Even though ... [tamoxifen] cut the risk of breast cancer in half, we got little use out of it because of the rare side effects," said the National Cancer Institute's Dr. Ford. "Now we're able to show that raloxifene, a drug already in widespread use to prevent and treat osteoporosis, has the additional benefit of preventing breast cancer with fewer serious side effects."

Staff writer Laura Beil contributed to this report.

E-mail eramshaw@dallasnews.com

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Source: The Dallas Morning News

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