Tamoxifen use is associated with an increased risk of endometrial cancer. A new study has found that this risk is similar in pre- and postmenopausal women, increases with duration of use, and does not diminish through 5 years of follow-up after the treatment ends.

The study was published in the Journal of the National Cancer Institute.

Anthony J. Swerdlow, D.Sc., of the Institute of Cancer Research in Sutton, England, and colleagues conducted a case-control study in Britain of 813 patients who had endometrial cancer following breast cancer diagnosis and 1,067 control subjects who had breast cancer but not subsequent endometrial cancer.

Overall, tamoxifen treatment was associated with 2.4 times the risk of endometrial cancer compared with no treatment. The risk increased with the duration of treatment and did not diminish in the 5 years following the end of treatment. The risk was similar in pre- and postmenopausal women.

The authors write that, until further data are available, their results "suggest that the associated risk of endometrial cancer makes treatment with tamoxifen beyond 5 years questionable."

SOURCE:
Journal of the National Cancer Institute, March 2, 2005