Tamoxifen therapy should last 5 years.

The much-criticized drug tamoxifen-a synthetic hormone widely prescribed to prevent recurrences of breast cancer-should be taken for 5 years after early-stage cancers are removed and should then be stopped, two new studies show.

Tamoxifen has been engulfed in controversy ever since several major studies detected a steep increase in the incidence of uterine cancer among women taking the drug (SN: 4/16/94, p. 247). In March, the World Health Organization formally labeled tamoxifen a carcinogen (SN: 3/2/96, p. 132).

Now, a Swedish study of 3,887 women indicates that those who took tamoxifen for 5 years had fewer recurrences of breast cancer-and fewer related deaths-than women who took the drug for just 2 years, says Lars E. Rutqvist of Karolinska Hospital in Stockholm.

A U.S. study of 2,818 women, known as the National Surgical Adjuvant Breast and Bowel Project, found that the benefits of 5 years' worth of tamoxifen therapy persisted for 5 years after women stopped taking the drug, reports Bernard Fisher of the University of Pittsburgh School of Medicine. Both studies appear in the Nov. 6 Journal of the National Cancer Institute. A second phase of the U.S. study, designed to assess the benefits of taking tamoxifen for a decade, was stopped last December, 6 years early.

Fisher says the results failed to show any additional advantage of a longer course of treatment-or any likelihood that a longer course would be worth the accompanying risk of uterine cancer. Of the U.S. women treated with tamoxifen, 21 developed uterine cancer in the first 5 years, while 17 developed the cancer in the 5 years after treatment. Only four of the women who did not receive tamoxifen developed uterine cancer.

In an accompanying editorial, Sandra Swain of the Greater Washington (D.C.) Area Comprehensive Breast Center, called a 5-year limitation on tamoxifen therapy "prudent," since the risks and benefits of a longer course of treatment remain uncertain.