Objective: To assess the relationship between low-dose tamoxifen, usage and endometrial cancer in breast cancer patients.
Methods: In this case-control study, the records of the 1017 patients treated at Wilford Hall Medical Center for primary breast cancer between 1978 and 1989 were reviewed. Dose and duration of tamoxifen therapy were recorded as well as the presence of a uterus. Potential confounding variables including diabetes mellitus, hypertension, age, weight, tobacco use, and family history of breast or gynecologic cancer were recorded.
Results: Of the 1017 patients in the study, 56 had inadequate records and 375 had undergone a prior hysterectomy and these patients were excluded from the study, leaving 586 eligible patients. Of these 586 women with primary breast cancer and no previous hysterectomy, 108 patients had received tamoxifen, 10 mg twice a day for greater than 1 year. Four of the 108 patients subsequently developed endometrial adenocarcinoma. Four hundred seventy-eight breast cancer patients did not receive tamoxifen and 4 later developed endometrial adenocarcinoma. The odds ratio for the development of endometrial cancer when exposed to tamoxifen was 15.2 with a 95% confidence interval of 2.8-84.4. The patients exposed and not exposed to tamoxifen were compared for potential confounding variables and after controlling for the potential confounders, tamoxifen was found to be an independent risk factor for the development of endometrial cancer.
Conclusions: Low-dose tamoxifen when given for greater than 1 year is associated with secondary endometrial cancer in patients with primary breast cancer.