The osteoporosis drug raloxifene is as effective as tamoxifen in preventing invasive breast cancer in postmenopausal women, according to initial results of the Study of Tamoxifen and Raloxifene (STAR) trial. The large, randomized, double-blind trial also determined that women taking raloxifene experienced fewer side effects than did those taking tamoxifen.
Raloxifene is approved for treating and preventing osteoporosis in postmenopausal women. At present, tamoxifen is the only drug approved for reducing breast cancer risk in pre- and postmenopausal women.
“This is good news for women,” said Dr. Leslie Ford, associate director for clinical research in the National Cancer Institute's Division of Cancer Prevention. “We think that this gives women a real choice for addressing two of the leading causes of morbidity and mortality as they age: breast cancer and fractures. … We can't advocate for the off-label use of drugs, but we anticipate that the company that makes raloxifene will be requesting an approval from the [Food and Drug Administration] for breast-cancer risk reduction.”
In the STAR trial, 167 of the 9,745 women in the raloxifene group and 163 of the 9,726 women in the tamoxifen group developed invasive breast cancers. There were no significant differences between the two groups in the risk of developing invasive breast cancer, which was the primary outcome of the trial.
For every 1,000 women similar to the high-risk women enrolled in the STAR trial, about 40 would be expected to develop breast cancer within 5 years if they did not take either drug. The risk would be decreased to about 20 cases of breast cancer for every 1,000 women within 5 years if they took either tamoxifen or raloxifene.
Women taking raloxifene had 36% fewer uterine cancers and 29% fewer blood clots than the women who took tamoxifen.
Dr. D. Lawrence Wickerham, associate chair of the National Surgical Adjuvant Breast and Bowel Project, characterized the results in unusually blunt terms. “We think raloxifene is the winner of this trial,” he said at a joint press briefing held by the National Cancer Institute and the National Surgical Adjuvant Breast and Bowel Project. The results have not yet been published. Additional data will be presented at the 42nd annual meeting of the American Society for Clinical Oncology (ASCO) to be held in Atlanta, Ga., in June.
The 19,471 women for whom complete information was available took tamoxifen or raloxifene daily for an average of 47 months. The average age of the women in the study was 58. There were no statistically significant differences in the number of fractures of the hip, wrist, and spine, with 100 for in the tamoxifen group and 96 in the raloxifene group.
Raloxifene proved inferior to tamoxifen in only one important measure. Tamoxifen has previously been shown to reduce by about half the incidence of lobular carcinoma in situ (LCIS) and ductal carcinoma in situ (DCIS). Of the women taking tamoxifen, 57 developed LCIS or DCIS, compared with 81 of the women taking raloxifene.
The STAR study has been supported to date by $88 million from the National Cancer Institute and $30 million from Eli Lilly & Co., the maker of raloxifene. Both Eli Lilly and AstraZeneca Pharmaceuticals, the maker of tamoxifen, provided their drugs and matching placebos free of charge.