Patients receive topotecan intravenously (IV) over 30 minutes on days 1, 8, 15, 22, and 29. Treatment repeats every 42 days for up to 6 courses in the absence of disease progression or unacceptable toxicity. Cohorts of 3-6 patients receive escalating doses of topotecan until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that at which 2 of 3 or 2 of 6 patients experience dose-limiting toxicity. A total of 6 patients will be treated at the MTD.