Tamoxifen Pharmacokinetics and CYP2D6 Polymorphisms in Asian Women With Hormone Receptor Positive Breast Cancer

Tamoxifen Pharmacokinetics and CYP2D6 Polymorphisms in Asian Women With Hormone Receptor Positive Breast Cancer

We hypothesized that subjects with CYP2D6*10 alleles may have a lower steady state levels of endoxifen due to reduced conversion of tamoxifen to endoxifen.

Primary objectives:

• To determine the steady state pharmacokinetics of tamoxifen and its metabolites
• To test the effects of genetic polymorphisms of CYP2D6 on plasma concentration of tamoxifen and its metabolites in hormone receptor positive women who are taking tamoxifen as adjuvant treatment for breast cancer.

Inclusion Criteria:

• Signed informed consent.
• At least 18 years of age.
• On tamoxifen for at least 3 months for adjuvant therapy.
• On a stable diet for past 1 week before blood sampling.
• Compliant with tamoxifen medication.
• Completed adjuvant chemotherapy and/or adjuvant radiation therapy.

Exclusion Criteria:

• Patients should not be on the list of medications for the last 1 week before accrual to the study