For women without osteoporosis who are at high risk of breast cancer, tamoxifen ... remains the 'gold standard.'

The randomized, double-blind Multiple Outcomes of Raloxifene Evaluation (MORE) trial found that in postmenopausal women with osteoporosis, four years of treatment with raloxifene was associated with a 72% reduction in breast cancer incidence compared with placebo.

The Continuing Outcomes Relevant to Evista (CORE) trial was designed to examine the effect of an additional four years of treatment with raloxifene in the same group of women.

Increase in Embolisms

In the CORE trial, more than 4,000 women who had been part of the MORE trial continued taking either 60 mg/day of raloxifene, if they had been assigned to the raloxifene group in the MORE trial, or a placebo, if they had been assigned to the placebo group.

Silvana Martino, D.O., of the Cancer Institute Medical Group in Santa Monica, Calif., and colleagues report that after the four years of the CORE trial, incidence of invasive breast cancer for women taking raloxifene was reduced by 59% compared with women taking the placebo, and incidence of estrogen-receptor (ER)-positive invasive breast cancer was reduced by 66%.

Over the entire eight years of MORE and CORE, the incidence of invasive breast cancer and ER-positive invasive breast cancer were reduced by 66% and 76%, respectively. There was no difference between the two groups in incidence of either ER-negative invasive breast cancer or noninvasive breast cancer. In both the MORE and CORE trials, there was a twofold increase in venous thromboembolic events, such as pulmonary embolism, among women taking raloxifene.

Tamoxifen Remains 'Gold Standard'

"These data demonstrate that the incidence of ER-positive invasive breast cancer continues to be reduced through eight years of raloxifene treatment in postmenopausal women with osteoporosis," the authors write. "The effect of raloxifene on breast cancer incidence is currently being evaluated in postmenopausal women at high risk for heart disease in the Raloxifene Use for The Heart (RUTH) trial and in postmenopausal women at high risk for breast cancer in the STAR [Study of Tamoxifen and Raloxifene] trial."

In an editorial, Powel Brown, M.D., Ph.D., of the Baylor College of Medicine in Houston, and colleagues note that the effect of raloxifene treatment in the CORE trial may be confounded by several factors, but write that the results of the CORE and MORE trials support the conclusion that raloxifene reduces the risk of breast cancer.

However, the authors write, "For women without osteoporosis who are at high risk of breast cancer, tamoxifen, in our opinion, remains the 'gold standard' chemoprevention agent to reduce the risk of breast cancer in high-risk pre- and postmenopausal women. We anticipate that the results of several large-scale chemoprevention trials will help clarify the role of raloxifene, as well as other hormonal agents, for breast cancer prevention."