Background: Breast cancer prevention with tamoxifen in high-risk women is limited due to concerns of endometrial cancer and thromboembolism. We report the risk of endometrial cancer, deep vein thrombosis and pulmonary embolism in women <50 years given tamoxifen for breast cancer prevention.
Methods: We searched the Cochrane Central Register of Controlled Trials and National Library of Medicine for published data from January 1970 to December 2010. We contacted principal investigators of clinical trials, and searched Grey literature and conference proceedings for unpublished data. We reviewed three breast cancer prevention trials comparing tamoxifen (20mg per day) with placebo for five years in high-risk women <50 years. The absolute risk and relative risk (RR) for each outcome were estimated.
Results: The RR for endometrial cancer in women <50 years given tamoxifen is 1.19 (95% CI, 0.53-2.65; p=0.6) as compared to the placebo. The RR for deep vein thrombosis with tamoxifen is 2.30 (95% CI, 1.23-4.31; p=0.009) in the active phase of treatment. The risk decreases to 1.00 (95% CI, 0.38-2.67; p=0.9) in the follow-up phase. The RR for pulmonary embolism with tamoxifen is 1.16 (95% CI, 0.55-2.43; p=0.6).
Interpretation: The risk of endometrial cancer, deep vein thrombosis and pulmonary embolism is low in women <50 years who take tamoxifen for breast cancer prevention. The risk decreases from the active to follow-up phase of treatment. Education and counseling are the cornerstones of breast cancer chemoprevention.
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