Long-term toxicity of tamoxifen.

Long-term tamoxifen has generally only few and usually mild adverse side effects. More serious, potentially life-threatening toxicities are rare. Aside from the ocular effects, most documented side effects appear to be related to the estrogenic properties of tamoxifen, for instance, thrombembolic disease and endometrial cancer. On the other hand, these properties may also be beneficial, for instance, they may contribute to a decreased risk of cardiac disease and osteoporosis. The potential association between tamoxifen and other possibly estrogenic side effects such as liver cancer and tamoxifen-induced tumor growth in patients with acquired tamoxifen resistance remain controversial.