Epirubicin is a common chemotherapy medication used in the treatment of breast cancer. However, chemotherapy dosing is calculated based on people's height and weight, which may not be the most accurate way. The purpose of this study is to see if epirubicin dosing based on people's genetic profiles is better than the usual methods.

Inclusion Criteria:

1. Female patients with histologically confirmed non-metastatic invasive breast cancer who are scheduled to receive at least three cycles of FEC100 in the adjuvant or neoadjuvant setting
2. Documented pathological evaluation of the breast cancer for hormone receptor (estrogen receptor [ER], progesterone receptor [PR] and HER-2 status
3. Eastern Cooperative Oncology (ECOG) performance status of ≤ 2
4. A Left Ventricular Ejection Fraction (LVEF) ≥ 50%.

Exclusion Criteria:

1. Uncontrolled congestive heart failure (CHF) or angina, history of myocardial infarction within 2 months before study enrollment, or cardiac functional capacity Class III or IV as defined by the New York Heart Association Classification.
2. Psychiatric disorder(s) that would interfere with consent, study participation, or follow up.