• Patients must have histologically or cytologically confirmed small cell lung cancer

• Patients must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for non-nodal lesions and short axis for nodal lesions) as \>20 mm with conventional techniques or as \>10 mm with spiral CT scan. See Section 8for the evaluation of measurable disease.

• Patient must have failed or found to be intolerant of standard frontline platinum-based regimens and not more than two lines of cytotoxic chemotherapy treatment in total for extensive stage disease. Maintenance immunotherapy counts as part of the frontline therapy, while prior chemotherapy for limited stage disease will not count toward this total if completed more than 12 months before initiation of protocol therapy. Retreatment with the original chemotherapy regimen for sensitive relapsed SCLC counts as a separate line of treatment.

• Adult patients with age \>18 years. Because no dosing or adverse event data are currently available on the use of arsenic trioxide in patients \<18 years of age, children are excluded from this study but will be eligible for future pediatric single-agent trials, if applicable.

• Ability to tolerate oral medicine

• ECOG performance status ≤2

• Patients must have normal organ and marrow function as pre-defined

• Negative serum pregnancy test within 48 hours before starting study treatment in women with childbearing potential

• Women of child-bearing potential and men must agree to use adequate contraception.

⁃ Ability to understand and the willingness to sign a written informed consent document.

⁃ Both men and women and members of all races and ethnic groups are eligible for this trial.