Introduction: Increased thromboembolic disorders and chemotherapy-induced thromboembolic events are well known phenomena in patients with breast cancer. Antithrombin III (AT III) inactivates thrombin, resulting in increased thrombin-antithrombin (TAT) levels. Activated factor X cleaves prothrombin and thrombin, resulting in increased levels of prothrombin fragment 1 + 2 (F 1 + 2). Increased TAT and F 1 + 2 levels show coagulation activation. The aim of this study was to examine plasma levels of TAT and F 1 + 2 and the effect of anthracycline-based chemotherapy on plasma TAT and F 1 + 2 in patients with operable breast cancer.