Inclusion Criteria:

1. Histologically or cytologically confirmed diagnosis of SCLC, which has relapsed after
first line chemotherapy for extensive-stage SCLC or first-line chemoradiotherapy for
limited-stage SCLC.

2. Have received one, and only one, prior chemotherapy or chemoradiotherapy regimen for
either newly diagnosed extensive-stage disease or limited-stage disease.

3. Prior therapies must be completed at least 4 weeks prior to enrollment and patients
must have recovered from all acute toxicities.

4. Measurable disease by RECIST.

5. ECOG performance status of 0-2.

6. At least 18 years of age.

7. Adequate bone marrow function as defined by absolute neutrophil count of greater than
or equal to 1,500/mm^3 and platelets of greater than or equal to 100,000/mm^3.

8. AST (SGOT) and ALT (SGPT) levels no greater than 3 x the institutional ULN, and total
bilirubin less than or equal to 1.5 x ULN.

9. Serum creatinine less than or equal to 1.5 x ULN, or creatinine clearance greater
than or equal to 60 mL/min (Cockcroft-Gault formula) for patients with serum
creatinine levels > 1.5 x ULN.

10. Able to understand and show willingness to sign a written informed consent document.

Exclusion criteria:

1. Patient has Gilbert's Syndrome.

2. Prior chemotherapy or radiotherapy within 4 weeks (6 weeks for nitrosoureas or
mitomycin C) prior to entering the study.

3. Lack of recovery from adverse effects due to agents administered more than 4 weeks
prior to study entry.

4. Concurrent use of other investigational agent.

5. History of brain metastases or spinal cord compression, unless irradiated a minimum
of 4 weeks before study entry and stable without requirement for corticosteroids for
> 1 week.

6. Prior exposure to topoisomerase 1 inhibitors (i.e., irinotecan, topotecan,
camptothecin).

7. Concurrent serious infections requiring parenteral therapy.

8. Pregnant or of childbearing potential and not using methods to avoid pregnancy. A
negative pregnancy test (urine or serum) must be documented at baseline for women of
childbearing potential. Patients may not breast-feed infants while on this study.

9. Significant cardiac disease including heart failure that meets New York Heart
Association (NYHA) class III and IV definitions, history of myocardial infarction
within one year of study entry, uncontrolled dysrhythmias or poorly controlled
angina.

10. History of serious ventricular arrhythmia (VT or VF, greater than or equal to 3 beats
in a row), QTc greater than or equal to 450 msec for men and 470 msec for women, or
LVEF less than or equal to 40% by MUGA or ECHO.