Survival impact of adjuvant tamoxifen on competing causes of mortality in breast cancer survivors, with analysis of mortality from contralateral breast cancer, cardiovascular events, endometrial cancer, and thromboembolic episodes.
PURPOSE This study provides estimates of the effect of tamoxifen treatment on mortality from four conditions known to be affected by tamoxifen in women who survive their breast cancer: contralateral breast cancer, cardiovascular events, endometrial cancer, and thromboembolic events. These estimates are in addition to tamoxifen's impact on primary breast cancer mortality. METHODS The effects of tamoxifen were calculated by the use of the published relative risk (RR) rates of the four conditions as affected by adjuvant tamoxifen and their application to the respective Canadian age-specific mortality rates for the same conditions. The final mortality impact of tamoxifen was expressed as net mortality difference between users and nonusers of tamoxifen. RESULTS At 10 years of follow-up, the sum of avoided deaths (contralateral breast cancer, cardiovascular events) and excess deaths (uterine cancer, thromboembolic episodes) resulted in an overall (net) mortality reduction because of tamoxifen use, with 3 to 41 avoided deaths per 1,000 tamoxifen-treated patients who were 50 to 80 years of age. With the follow-up projected until the age of 90 years, the numbers of avoided late deaths attributed to tamoxifen ranged from 38 to 56 per 1,000 patients. CONCLUSION Our calculations that pertain to late breast cancer survivors indicate that there is a more substantial mortality reduction as a result of deaths avoided from contralateral breast cancer and cardiovascular events, despite the moderately increased mortality from endometrial cancer and thromboembolic episodes. The overall tamoxifen-associated mortality reduction occurs, in different magnitudes, in patients of all ages from 50 to 80 years at diagnosis of the primary breast cancer.