TAMOXIFEN-ASSOCIATED VENOUS THROMBOSIS AND ACTIVATED PROTEIN-C RESISTANCE DUE TO FACTOR-V-LEIDEN

BACKGROUND. Thromboembolic events are well recognized complications of cancers and their treatment. Tamoxifen, an antiestrogen used in the t reatment of breast carcinoma and other malignancies, has been associat ed with thrombotic events. Activated protein C resistance due to Facto r V Leiden is the most prevalent inherited prothrombotic defect in pop ulations of European descent and has been reported as a major cofactor in the development of thrombosis in women receiving estrogens. METHOD S. The authors report three patients who developed thromboembolic comp lications while receiving tamoxifen. These patients were studied for t he presence of activated protein C resistance by coagulation assay and the presence of Factor V Leiden by molecular analysis. RESULTS. All t hree patients had resistance to activated protein C by coagulation ass ay and were determined to be heterozygous for Factor V Leiden by molec ular analysis. CONCLUSIONS. The authors propose that inheritance of Fa ctor V Leiden significantly increases the risk of thrombosis in patien ts who receive tamoxifen therapy. All patients prescribed tamoxifen sh ould be carefully questioned regarding personal and family histories o f thrombosis and, when indicated, screened for Factor V Leiden. (C) 19 97 American Cancer Society.