Data from additional years of follow-up of a large randomized placebo-controlled clinical trial of tamoxifen for the prevention of breast cancer confirm that the drug reduces the risk of invasive and noninvasive breast cancer, according to a report that appears in the current issue of the Journal of the National Cancer Institute.
The National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention Trial (P-1) began in 1992. More than 13,000 women aged 35 years and older who were at high risk for breast cancer were randomly assigned to receive either a placebo or tamoxifen for 5 years. In 1998, the study's independent data monitoring committee recommended that the study be unblinded. An overall 49% reduction in breast cancer risk was observed in women taking tamoxifen. Participants were informed of whether they were taking a placebo or tamoxifen so that women who were taking placebo could be given the option to take tamoxifen.
The initial findings from the study--which appeared in the Sept. 16, 1998, issue of the Journal of the National Cancer Institute--indicated that tamoxifen reduced the risk of invasive and noninvasive breast cancer. Tamoxifen was also found to reduce the risk of osteoporotic fractures but to increase the risks of endometrial cancer and thromboembolism.