Tamoxifen and Metabolite Concentrations in Serum and Breast Cancer Tissue during Three Dose Regimens in a Randomized Preoperative Trial

Abstract

Estrogen agonistic effects of tamoxifen on SHBG decreased with lower dosage, whereas tamoxifen effects on Ki-67 expression did not change. This together with a >10-fold variation in serum tamoxifen concentrations and a serum to tissue concentration relationship suggest that tamoxifen treatment may be improved by administration of lower doses and therapeutic drug monitoring.