Taking Evista (raloxifene) for longer than four years reduces the risk of invasive breast cancer beyond that already found in earlier studies that looked at four years of treatment, findings from a new follow-up study indicate.

In the Multiple Outcomes of Raloxifene Evaluation (MORE) trial, treatment with Evista for four years reduced the risk of invasive breast cancer in postmenopausal women with osteoporosis.

In the new study, called the Continuing Outcomes Relevant to Evista (CORE) trial, the risk continued to drop over four additional years of treatment.

CORE involved 5,213 women who participated in MORE and were randomly assigned to receive either Evista or placebo, according to the report in the Journal of the National Cancer Institute.

Women treated with Evista in MORE were given a dose of 60 milligrams or 120 milligrams per day, but in CORE they all received 60 milligrams per day, lead author Dr. Silvana Martino, from the Cancer Institute Medical Group in Santa Monica, California, and colleagues write.

In CORE, treatment with Evista was associated with a 59-percent drop in overall breast cancer and a 66-percent drop in estrogen receptor-positive breast cancer over four years.

In contrast, Evista therapy seemed to have no effect on the rates of estrogen-receptor-negative breast cancer.

For the combined eight-year study period, Evista therapy cut the rate of overall and estrogen receptor-positive invasive breast cancer by 66 percent and 76 percent, respectively.

However, Evista therapy was also associated with an increased risk of blood clots. Throughout the eight-year period, the rate of blood clots among Evista users was about double that seen in women in the placebo group.

In a related editorial, Dr. Powel Brown and colleagues, from Baylor College of Medicine in Houston, comment that the findings of these two clinical trials suggest that Evista is “a reasonable choice to treat osteoporosis and also to reduce the risk of breast cancer” in postmenopausal women with osteoporosis.

Further studies, however, are needed to determine if the drug is also useful for women without osteoporosis, but at increased risk for breast cancer, the editorialists add.

SOURCE: Journal of the National Cancer Institute, December 1, 2004.