This is a study to explore how well the combination of LY231514 and Gemcitabine work together in patients with breast cancer that has spread beyond the location of the original tumor. Patients must have previously received treatment with anthracycline and taxane chemotherapy drugs.

Gemcitabine is given by vein over 30 minutes on days 1 & 8 of each 21-day cycle. LY231514 is also given by vein over 10 minutes on day 8, following the Gemcitabine injection. Vitamin supplementation with oral folic acid and injectable B12 is initiated 7-10 days prior to the first dose of LY231514, and continuing throughout the patient's participation. Vitamin B12 is administered approximately every 9 weeks after the first injection. Appropriate antiemetic medication should be given to all patients. Dexamethasone 4mg PO twice daily is given for 3 days per cycle, beginning 1 day prior to LY231514 dosing. This is given to prevent or lessen the possibility of a rash.

Inclusion Criteria:

• confirmed diagnosis of breast cancer
• measurable disease
• received prior anthracycline and taxane
• life expectancy > 3 months
• acceptable lab results

Exclusion Criteria:

• >3 prior regimens
• prior treatment with protocol drugs
• prior (pelvic) radiation
• active CNS metastasis
• inability to take oral vitamins