OBJECTIVES:
Primary
* To determine how the increase of tamoxifen citrate dose influences the level of its major metabolites in patients with hormone-sensitive breast cancer.
Secondary
* To characterize the population pharmacokinetic profile
* To investigate the role of the other CYPs
* To assess the relation between clinical symptoms and CYP2D6 genotypes and/or active metabolites levels
* To explore the correlation between genotypes/metabolites levels and clinical outcomes in terms of tumor relapse.
* To assess the feasibility, efficacy, and safety of concentration-guided adjustment of tamoxifen citrate dosage.
* To conduct other exploratory analysis based on the eventual new data coming up in the future.
OUTLINE: Patients receive oral tamoxifen citrate (at a dose of 40 mg/day) daily for 4 months in the absence of disease progression or unacceptable toxicity.
Blood samples are collected for PK, genotyping, phenotyping, and further analysis.
