Inclusion Criteria:

- Females, age 18 years of age or older, of all racial and ethnic origins that are
scheduled to receive the first cycle of a single intravenous dose of doxorubicin (30
minute infusion) and cylcophosphamide (30 minute infusion) as part of standard
medical care for breast cancer. English and/or Spanish speaking participants are
eligible to participate.

Exclusion Criteria:

- Pregnant or nursing or unwilling to use a reliable contraception method during the
study. The effects of doxorubicin and cyclophosphamide on pregnancy are unknown. In
addition, the metabolic changes that accompany pregnancy may alter the
concentration-time profile of doxorubicin or cyclophosphamide, so that the pregnancy
and post-partum state would be a confounding variable.

- Participants unwilling to comply with study procedures.

- CrCl < 10 ml/min

- Participants requiring peritoneal or hemodialysis

- Serum bilirubin > 1.19 mg/dL

- Receipt of the following drugs that: a) Alter doxorubicin concentrations:
carbamazepine, cyclosporine, fosphenytoin, paclitaxel, phenytoin, sorafenib,
valspodar, verapamil; b) Alter cyclophosphamide concentrations: cyclosporine,
nevirapine, ondansetron; c) All other drugs will be reviewed during screening of the
patient