Combination Chemotherapy With or Without Filgrastim in Treating Patients With Previously Untreated Extensive-Stage Small Cell Lung Cancer

RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Colony-stimulating factors such as filgrastim may increase the number of immune cells found in bone marrow or peripheral blood and may help a person's immune system recover from the side effects of chemotherapy. PURPOSE: Phase II trial to compare the effectiveness of combination chemotherapy with or without filgrastim in treating patients who have extensive-stage small cell lung cancer that has not been previously treated.

OBJECTIVES: * Determine the tolerability of topotecan and carboplatin with or without filgrastim (G-CSF) in patients with extensive stage small cell lung cancer. * Determine response and survival rates in patients treated with these regimens. OUTLINE: This is a multicenter study. The first 12 patients are assigned to 1 of 2 treatment regimens (6 per regimen). The next 33 patients receive treatment based on the toxicity experienced by the first 12. Regimen A: * Patients receive oral topotecan once daily on days 1-5, carboplatin IV over 30 minutes on day 5, and filgrastim (G-CSF) subcutaneously once daily beginning on day 6 or 7 and continuing for up to 10 days or until blood counts recover. * Patients are evaluated after the first 3-week course of chemotherapy. If no patient experiences unacceptable toxicity or febrile neutropenia, or no more than 1 patient experiences an absolute neutrophil count of less than 500/mm3 for more than 5 days, the next 6 patients begin treatment on regimen B. Otherwise, all patients receive treatment as in regimen A. Regimen B: * Patients receive topotecan and carboplatin as in regimen A. * Patients are evaluated after the first 3-week course of chemotherapy. If no patient experiences unacceptable toxicity or febrile neutropenia, the next 33 patients receive treatment as in regimen B; otherwise, patients receive treatment as in regimen A. Treatment for all patients repeats every 3 weeks for up to 6 courses in the absence of disease progression or unacceptable toxicity. Patients with disease progression limited to CNS only interrupt chemotherapy to have whole-brain radiotherapy (WBRT). Once WBRT is complete, chemotherapy resumes. Quality of life is assessed at baseline and at the beginning of each course of chemotherapy. Patients are followed every 3 months for 2 years and then every 6 months for 3 years. PROJECTED ACCRUAL: A total of 49 patients will be accrued for this study within 13.5 months.