Consequences of Factor V Leiden Mutation in Patients Treated with Adjuvant Tamoxifen

The most common hereditary hypercoagulability disorder in the U.S. is caused by the factor V Leiden (FVL) mutation, a dominant trait with an incidence of 5% in non-Hispanic whites and 1% to 2% in blacks. Adjuvant tamoxifen therapy is associated with higher risk for thrombotic events compared with placebo (1.7% vs. 0.4%), with most events occurring in women aged >50. Adjuvant chemotherapy for breast cancer also has prothrombotic effects; moreover, the combination of adjuvant chemotherapy and tamoxifen results in an additive increase in risk for thrombotic events. The FVL mutation is associated with further excess risk for thrombotic events in individuals who are already at risk. To evaluate whether this effect of the FVL mutation applied to …