The influence of tamoxifen in vivo on the main natural anticoagulants and fibrinolysis.

The long-term effects of tamoxifen on alterations in haemostasis which could lead towards thrombosis were investigated in 149 women who were disease-free for at least 5 years following mastectomy for breast cancer. All participants were randomized to receive tamoxifen as a post-surgical adjuvant treatment (89 patients, treated group) or not (60 patients, controls) for at least 2 years. 5.62% of the cases treated with tamoxifen suffered a venous thrombosis, while no thromboembolism was reported in the control group. No significant differences were observed between groups in the global clotting times, fibrinogen, fibrinolytic factors, or in the concentration of the main natural anticoagulants, antithrombin III (AT-III), protein C (PC) and protein S (PS). However, when the treated group was sub-divided, current users (n= 18) of the drug (median treatment duration 72 months) had significantly lower AT-III (P