This study will examine how the body handles etoposide, a drug used to treat breast cancer. The knowledge gained may lead to more effective use of the drug with fewer side effects in the future.
Breast cancer patients who are receiving etoposide as part of their treatment may participate in this study. Patients will have 18 blood samples (about a teaspoon or less each) drawn over a 72-hour period during and after their infusion of etoposide. The initial blood samples cannot be taken from the same intravenous line (small tube placed in a vein) used to deliver the etoposide, so a second line may have to be placed temporarily to obtain these samples.
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Etoposide is a topoisomerase II inhibitor that has a broad range of anticancer activity at conventional doses (100 mg/m(2) daily x 5 days) and is administered in high doses (greater than 1200 mg/m(2)) as a component of pre-transplant myeloablative chemotherapy regimens. Etoposide pharmacokinetics are linear over a 30-fold dose range, but disposition is highly variable. Etoposide is highly protein bound (95%) to albumin, but protein binding (and therefore free drug concentrations) vary widely in cancer patients. Etoposide is eliminated by metabolism and renal excretion, which may also contribute to the variability. The pharmacokinetics of etoposide will be studied in patients receiving high-dose etoposide as part of their pre-transplant preparative regimen, and pharmacokinetic parameters generated from pharmacokinetic modeling will be correlated with clinical and laboratory characteristics and toxicity in order to develop more rational dosing methods.