PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent immunotherapy Chemotherapy: No prior topotecan, other camptothecin analogs, or etoposide At least 1 prior cisplatin/paclitaxel based regimen At least 3 weeks since prior chemotherapy and recovered No more than 2 prior cytotoxic chemotherapy regimens No other concurrent chemotherapy Endocrine therapy: No concurrent hormonal therapy for cancer Radiotherapy: At least 3 weeks since prior radiotherapy to no more than 10% of the bone marrow and recovered No concurrent radiotherapy Surgery: Not specified Other: At least 28 days or 5 half lives since prior investigational drugs (including cytotoxic drugs) No concurrent metoclopramide or cisapride for maintaining gastric motility or emptying No chronic H2 antagonists, proton pump inhibitors, or antacids for gastritis, gastroesophageal reflux disease, or gastric or duodenal ulcers Intermittent antacids allowed, if no antacids 6 hours prior to and 90 minutes after topotecan