Tamoxifen therapy for breast cancer and endometrial cancer risk

Abstract

Background: Tamoxifen is effective in treating breast cancer, reduces breast cancer incidence among high-risk women, and is associated with increased endometrial cancer risk. This study was designed to examine the possible modifying effects of endometrial cancer risk factors on the tamoxifen-endometrial cancer association. Methods: We conducted a case- control study of endometrial cancer (324 case patients and 671 individually matched control subjects) nested within a population-based cohort of patients with breast cancer diagnosed from 1978 through 1992 within four regions of the United States. We obtained information on breast cancer treatment and endometrial cancer risk factors through interviews and reviews of medical records. All P values reported are two-sided. Results: Endometrial cancer risk was associated with tamoxifen therapy for breast cancer (odds ratio = 1.52; 95% confidence interval [CI] = 1.07-2.17). Risk increased with duration of tamoxifen use (P for trend = .0002). Women with more than 5 years of exposure to tamoxifen had 4.06-fold greater odds of developing endometrial cancer than nonusers (95% CI = 1.74-9.47). Prior use of estrogen replacement therapy (ERT) increased risk associated with tamoxifen use (P for homogeneity of trends