Inclusion Criteria

Histological or cytological confirmed extensive-stage SCLC with availability of representative baseline tumor tissue

Patients who progressed after at least 1 platinum-based chemotherapy regimen. Patients with platinum resistance (defined as recurrence or progression of disease within 90 days of completion of the platinum-based regimen) are eligible.

Treatment to be initiated at least 2 weeks since last dose of prior systemic anticancer therapy (chemotherapy, radiation, and/or surgery).

Recovery to grade 1 of any clinically significant toxicity (excluding alopecia) prior to initiation of study drugs.

Female patients of childbearing potential have a negative pregnancy test at baseline.

Women of childbearing potential (i.e., menstruating women) must have a negative urine pregnancy test (positive urine tests are to be confirmed by serum test) documented within 14 days of study registration and within the 24-hour period prior to the first dose of study drug.

Sexually active women of childbearing potential enrolled in the study must agree to use 2 forms of accepted methods of contraception during the course of the study and for 23 weeks after their last dose of study drug. 

For male patients who are sexually active and who are partners of premenopausal women: agreement to use 2 forms of contraception during the treatment period and for 31 weeks after the last dose of study drug.

Exclusion Criteria

Active interstitial lung disease (ILD) or pneumonitis or a history of ILD or pneumonitis requiring treatment with steroids

Pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial, starting with the pre-screening or screening visit through 23 weeks (female) or 31 weeks (male) after the last dose of study drug.

Must not have received PD-1, PD-L1 or CTLA-4 targeted therapy previously

Treatment with any investigational agent within 28 days prior to registration for protocol therapy.

Known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Patients with neurological symptoms must undergo a head computed tomography (CT) scan or brain magnetic resonance imaging (MRI) to exclude brain metastasis. Patients whose brain metastases have been treated may participate provided they show radiographic stability (defined as 2 brain images obtained after treatment to the brain metastases at least 4 weeks apart and show no evidence of intracranial progression)

Known history of human immunodeficiency virus (HIV) or active hepatitis B (by surface antigen expression or polymerase chain reaction [PCR]) or active hepatitis C (by PCR) infection.

Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to study registration.

Has active autoimmune disease that has required systemic treatment in the past 2 years (i.e., with use of disease modifying agents, corticosteroids, or immunosuppressive drugs) or a documented history of clinically severe autoimmune disease, or a syndrome that requires systemic steroids or immunosuppressive agents. Vitiligo, alopecia, hypothyroidism only requiring hormone replacement, psoriasis not requiring systemic treatment, celiac disease controlled by diet alone or conditions not expected to recur in the absence of an external trigger are permitted.

A condition requiring systemic treatment with corticosteroids (>10 mg daily prednisone equivalent) or other immunosuppressive medications within 14 days prior to administration of study drugs.

History of psychiatric illness or social situations that would limit compliance with study requirements. Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the patient's participation for the full duration of the trial, or is not in the best interest of the patient to participate, in the opinion of the treating investigator.

Prior malignancies (except non-melanoma skin cancers, and the following in situ cancers: bladder, gastric, colon, endometrial, cervical/dysplasia, melanoma, or breast) unless a complete remission was achieved at least 2 years prior to study entry.

Documented history of a cerebral vascular event (stroke or transient ischemic attack), unstable angina, myocardial infarction, or cardiac symptoms consistent with New York Heart Association (NYHA) Class III-IV within 6 months prior to their first dose of study drugs.

Evidence of ongoing inadequately controlled hypertension (defined as baseline systolic blood pressure >160 mmHg or diastolic blood pressure >100 mmHg).

Any active grade 3 or higher viral, bacterial, or fungal infection within 2 weeks of the first dose of the study drugs. Routine antimicrobial prophylaxis is permitted.