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 below that at which 2 of 6 patients experience dose limiting toxicity (DLT). Dose escalation of gemcitabine then continues in cohorts of 3-6 patients until the MTD is determined. The MTD is defined as the dose below that at which 2 of 6 patients experience DLT.