- The Washington Times - Monday, June 5, 2006

ATLANTA (AP) — Final results from a big study comparing two drugs for preventing breast cancer in high-risk women reveal surprises that challenge the government’s claim that one is clearly better.

The study compared the old standby, tamoxifen, to raloxifene, a newer drug so far approved only for preventing the bone disease osteoporosis. The government contends that raloxifene is safer.

At a press conference in April, the National Cancer Institute, which paid for the $88 million study, said both drugs were equally effective at lowering the risk of serious forms of breast cancer. But raloxifene users had 36 percent fewer uterine cancers and 29 percent fewer blood clots, making it a safer choice, government researchers said.

However, data made public yesterday show that the uterine cancer results were not statistically significant. Scientific standards have long held that such results only suggest trends and are not definitive.

Furthermore, so few blood clots occurred in the study that some doctors don’t think that result proves raloxifene is better. Also, it isn’t known whether raloxifene’s cancer-prevention benefit will last years after women stop taking the pills, as tamoxifen’s is known to do.

“There is some genuine controversy here,” said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society. Not everyone agrees “that there was a clear winner in this study,” he said.

The news generated heated discussions at an Atlanta meeting of the American Society of Clinical Oncology, where the study’s results were to have been reported first so other researchers could review them as they were released to the public. Instead, the cancer institute hastily called the press conference and didn’t disclose that some key results were not statistically significant.

Tamoxifen has been used for decades to treat and prevent breast cancer. It blunts estrogen, which fuels the growth of most tumors that occur after menopause, but also acts like estrogen elsewhere in the body and has been shown to raise the risk of blood clots and uterine cancer.

Raloxifene, sold as Evista by Eli Lilly and Company for osteoporosis, is thought to be less likely to cause these problems.

The study tested the drugs in nearly 20,000 postmenopausal women at high risk of breast cancer because of gene mutations, family history or other reasons. Raloxifene’s safety in premenopausal women is unknown.

Results were released yesterday at the cancer meeting and will be in the June 21 issue of the Journal of the American Medical Association.

The results:

• Invasive breast cancers: 168 among the 9,745 raloxifene users; 163 among the 9,726 who took tamoxifen.

• Noninvasive breast cancers: 57 in the tamoxifen group; 80 in raloxifene users.

• Uterine cancers: 36 among the 4,732 on tamoxifen; 23 in the 4,712 on raloxifene. Half of the women in the study had had a hysterectomy and, therefore, were not at risk of uterine cancer.

• Less serious forms of breast cancer developed in 57 women on tamoxifen and 80 on raloxifene.

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