Although tamoxifen has anti-estrogenic effects in the breast, it exerts estrogen-mimetic effects on the coagulation system and is associated with increased rates of venous thromboembolism (VTE). Risk of VTE is particularly high during the first 2 years of therapy and in those who require prolonged immobilization due to surgery (or travel). As a result, patients who take tamoxifen for primary prophylaxis (as in this patient with atypical ductal hyperplasia) should discontinue the medication 2-4 weeks prior to any surgery associated with a moderate or high risk of VTE (eg, hip replacement). Those on tamoxifen for cancer treatment should discuss perioperative cessation with their oncologist. Procedures associated with a low risk of VTE usually do not require tamoxifen cessation.
