RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. It is not yet known if topotecan is more effective given by infusion or by mouth.

PURPOSE: Randomized phase III trial to compare the effectiveness of topotecan given by infusion with that of topotecan given by mouth in treating patients who have small cell lung cancer that has relapsed following previous therapy.

OBJECTIVES: I. Compare the response rate, response duration, time to response, time to progression, and survival of patients with relapsed limited or extensive stage small cell lung cancer treated with oral vs intravenous topotecan. II. Compare the qualitative and quantitative toxicities of these treatment regimens in this patient population. III. Compare the quality of life in these patients.

OUTLINE: This is randomized, multicenter study. Patients are stratified according to gender, liver metastases (yes vs no), and duration of response to prior chemotherapy (6 months or less vs greater than 6 months). Patients are randomized to one of two treatment arms. Arm I: Patients receive topotecan IV over 30 minutes on days 1-5. Arm II: Patients receive topotecan orally on days 1-5. Treatment repeats every 3 weeks in the absence of unacceptable toxicity. Patients experiencing complete or partial response continue until progression or for at least 2 courses past maximal response. Patients with stable disease should receive at least 4 courses. Quality of life is assessed Patients are followed every 3 months.

PROJECTED ACCRUAL: A total of 300 patients (150 per treatment arm) will be accrued for this study.

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed limited or extensive stage small cell lung cancer (SCLC) Disease recurring at least 90 days following completion of first line chemotherapy Partial or complete response to first line therapy Must have at least one bidimensionally measurable non CNS lesion May be within a prior radiation port if at least 6 weeks since prior radiotherapy and progressing Brain and/or leptomeningeal metastases allowed if asymptomatic and not requiring corticosteroids

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: At least 2 months Hematopoietic: WBC at least 3,500/mm3 Neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9.0 g/dL (after transfusion, if needed) Hepatic: Bilirubin no greater than 2.0 mg/dL SGOT and SGPT no greater than 2 times upper limit of normal (ULN) (no greater than 5 times ULN if liver metastases present) Alkaline phosphatase no greater than 2 times ULN (no greater than 5 times ULN if liver metastases present) Renal: Creatinine no greater than 1.5 mg/dL OR Creatinine clearance at least 60 mL/min Other: No active uncontrolled infection No other malignancies within the past 5 years except curatively treated basal or squamous cell skin cancer, carcinoma in situ of the cervix, or stage I low grade prostate cancer No other severe medical conditions that would preclude study or cause exposure to extreme risk or decreased life expectancy No uncontrolled emesis No active peptic ulcer, diabetes mellitus, chronic gastritis, significant ascites, or other gastrointestinal (GI) conditions (e.g., removal of a portion of the stomach or recent GI obstruction) that would alter absorption or GI motility No history of allergic reactions to compounds chemically related to topotecan Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception for 3 months prior to, during, and at least 4 weeks after the study

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 3 months since prior immunotherapy No concurrent immunotherapy for SCLC Chemotherapy: See Disease Characteristics No prior topotecan Only one prior chemotherapy regimen allowed No other concurrent chemotherapy for SCLC Endocrine therapy: See Disease Characteristics Radiotherapy: See Disease Characteristics At least 24 hours since prior radiotherapy No concurrent radiotherapy for SCLC Surgery: At least 4 weeks since prior surgery Other: At least 30 days or five half lives since other prior investigational drugs No prior drugs (e.g., cisapride) that would alter absorption or GI motility No other concurrent investigational therapy for SCLC