NEW YORK, Jul 10 (Reuters) -- Tamoxifen may not be effective for the prevention of breast cancer in healthy women, according to two new British studies released on Friday. The findings appear to contradict an American study published earlier this year, that found that the drug could reduce the risk of cancer by 45% in women at high risk for the disease.
However, the new studies included fewer women -- just under 8,000 -- compared to more than 13,000 in the US trial. And in general, the women studied were younger, and had a relatively low-to-moderate breast cancer risk compared to those in the US trial.
Those factors could account for the different results, according to Dr. Kathleen I. Pritchard, who wrote an editorial accompanying the studies in the July 11th issue of The Lancet.
"The failure of these trials to confirm the results of the US study, however, casts doubt on the wisdom of the rush, at least in some places to prescribe tamoxifen widely for prevention," wrote Pritchard, of the University of Toronto in Canada.
In one study, conducted by Dr. U. Veronesi of the European Institute of Oncology in Milan, and colleagues, 5,408 women who had undergone hysterectomy took either tamoxifen or placebo and were followed for 46 months. When it came to breast cancer diagnosis, there was no difference between the two groups. However, a subgroup of women who were taking hormone replacement therapy in addition to tamoxifen did appear to have a lower risk of developing breast cancer. About 8 women out of 390 taking hormones and a placebo developed cancer, compared to 1 out of 362 taking hormones and tamoxifen.
In the study group as whole, women who took tamoxifen generally had a greater risk of vascular problems, such as blood clot formation, and elevated triglycerides, a blood fat, compared with controls -- an "unexpected finding," according to the researchers.
In the second study, Dr. Trevor Powles of the Royal Marsden NHS Trust in Surrey, UK and colleagues looked at 2,471 healthy women aged 30 to 70 with a family history of breast cancer. Women taking tamoxifen developed breast cancer at the same rate as those taking placebo during the 70 month study.
"The discrepancy in the results between Britain and America will only be sorted out by continuing the trials here," noted Powles during a press conference." This will allow us to evaluate the long-term risks and benefits of using tamoxifen in healthy women and to see which women may gain most benefit." SOURCE: Lancet 1998;352:80-81,90-101.