This is a non-randomized Phase 2 study testing pemetrexed and doxorubicin in combination for locally advanced or metastatic breast cancer. Both pemetrexed and doxorubicin have been combined with other drugs, but they have not yet been combined with each other. It is expected that the patient will benefit from the different mechanisms of action of the two drugs. However, there is no guarantee that the patient will benefit from this treatment.

Inclusion Criteria:

• Diagnosis of locally advanced or metastatic breast cancer that is not amenable to local treatment.
• Patients must be chemo-naive or have received only neoadjuvant and/or adjuvant chemotherapy.
• At least one measurable lesion.
• No chemotherapy within 4 weeks prior to enrollment.
• Signed informed consent from the patient.

Exclusion Criteria:

• Prior chemotherapy for metastatic breast cancer.
• Prior treatment with any anthracyclines or anthracenedione-containing regimen.
• Treatment within the last 30 days with any drug that has not received regulatory approval.
• Pregnancy and/or breast feeding.
• Inability or unwillingness to take folic acid or vitamin B12 supplementation.