OUTLINE: This is a dose-escalation study of topotecan in combination with fluorouracil. Patients receive topotecan as a 24-hour continuous infusion on days 1-14 in combination with fluorouracil IV and leucovorin calcium IV on days 1-5; course repeats every 4 weeks. Treatment continues in the absence of unacceptable toxicity or disease progression. In the absence of dose limiting toxicity (DLT) in the first cohort of 3 patients treated, subsequent cohorts each receive escalating doses on the same schedule. If DLT is observed in 2 of 3 patients or 2 of 6 patients at a given dose level, then dose escalation ceases and the next lower dose is declared the maximum tolerated dose.