Inclusion Criteria:

• Histologically or cytologically confirmed small cell lung cancer (SCLC). Mixed histology will not be eligible.
• Progression of disease after only one prior platinum containing chemotherapy regimen. Prior Regimen must not have contained irinotecan
• All patients must have measurable disease.
• Patients may have received prior radiation therapy but they must have recovered from all treatment-related toxicities.
• ECOG performance status 0-1
• Adequate hematologic function
• Adequate liver and renal function
• Ability to swallow oral medication

Exclusion Criteria:

• Patients with more than one prior regimen of chemotherapy or prior regimen that did not contain a platinum agent. Note: Patient who stopped prior therapy due to toxicity or had less than 2 cycles of platinum based therapy would not be eligible for the phase II portion of this study.
• Prior chemotherapy regimen containing irinotecan.
• Active secondary malignancy.
• Unstable or progressive brain metastases.
• Prior history of radiation therapy to > 25% of the bone marrow.
• Uncontrolled concurrent illness including, but not limited to: serious uncontrolled infection, symptomatic congestive heart failure (CHF), unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with the study requirements.
• Failure to recover from toxicities related to prior therapy (e.g., surgery, radiation, chemotherapy).