PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy OR Progression after stable disease or initial response to 1 prior chemotherapy regimen, including 1 preoperative or adjuvant chemotherapy regimen Endocrine therapy: Concurrent steroids allowed if dose is stable Radiotherapy: See Disease Characteristics At least 3 weeks since prior radiotherapy Surgery: See Disease Characteristics Other: No prior antifolates At least 7 days since prior folic acid supplements