This study is designed to determine the efficacy of the biweekly pemetrexed/gemcitabine regimen when given to patients with metastatic breast cancer. Each agent has well demonstrated antitumor activity in patients with locally advanced or metastatic breast cancer. In addition, in the phase I combination trial of the two agents, a durable tumor response was seen in one out of three heavily pretreated breast cancer patients (Adjei et al. 2000). Therefore, it is reasonable to expect that the combination of pemetrexed and gemcitabine administered may be associated with considerably more anti-tumor activity than either agent alone. If such activity is seen in this study, randomized studies comparing this combination with other active agents or combinations of active agents will be considered.

INCLUSION:

1. Have a performance status of 0 to 2 on the ECOG performance status schedule.
2. Patients may have had up to one prior systemic chemotherapy for metastatic disease is allowed. Prior adjuvant therapy is allowed if it has been more than one year since the end of therapy.
3. Patients must have measurable disease as defined by RECIST criteria (Therasse et al. 2000):
4. Have adequate organ function including the following

EXCLUSION:

1. Have serious concomitant systemic disorders (eg, active infection) that, in the opinion of the investigator, would compromise the safety of the patient or compromise the patient's ability to complete the study.