After interim analysis decided not to move forward with continuing the trial.

This phase II pilot trial studies how well gemcitabine and nivolumab work in treating participants with small cell lung cancer that has spread to other parts of the body after other treatments have failed. Drugs used in chemotherapy, such as gemcitabine, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Monoclonal antibodies, such as nivolumab, may interfere with the ability of tumor cells to grow and spread. Giving second-line gemcitabine and nivolumab may work better in treating participants with small cell lung cancer.

PRIMARY OBJECTIVES:

I. To compare response rate (RR) of gemcitabine and nivolumab (G+N) after 4 cycles (8 weeks) to historical controls treated with nivolumab alone.

SECONDARY OBJECTIVES:

I. To compare median overall survival (OS) of G+N to historical controls treated with nivolumab alone.

II. To compare median progression-free survival (PFS) of G+N to historical controls treated with nivolumab alone.

III. To evaluate for tolerability of G+N at each treatment cycle and then every 8 weeks after treatment is completed.

EXPLORATORY OBJECTIVES:

I. To correlate immunophenotypic changes among lymphocytes (quantitative measurements of CD4 and CD8 T-cells) with radiographic response and overall survival before treatment, after treatment and between 8-12 weeks after treatment.

II. Among those patients with tumor mutation burden (TMB) status available, to describe the association between TMB (low, medium, or high) and RR, OS, and PFS.

III. Assess the patient perspective of symptomatic adverse events using self-reported items from the National Cancer Institute (NCI) Patient Reported Outcomes-Common Terminology Criteria for Adverse Events (PRO-CTCAE).

OUTLINE:

Participants receive gemcitabine intravenously (IV) over 30 minutes and nivolumab IV over 60 minutes on day 1. Treatment repeats every 2 weeks for up to 4 courses in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, participants are followed up at 30 days, 6-10 weeks, and every 8 weeks thereafter.

Inclusion Criteria:

• Patients must have histologically or cytologically confirmed incurable SCLC and have had prior treatment with platinum-based chemotherapy. High-grade neuroendocrine tumors that are suspected to be of bronchopulmonary origin can be enrolled if they have had prior treatment with a SCLC chemotherapy regimen (e.g. platinum plus etoposide).
• Patients should not be demonstrating end-organ damage due to rapid progression of disease based on the most recent assessment of the treating physician.
• Patients must have radiographically measurable metastatic disease by Response Evaluation Criteria in Solid Tumors (RECIST) criteria.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
• Absolute neutrophil count >= 1,500/mcL.
• Platelets >= 100,000/mcL.
• Chemotherapy agents are known to be teratogenic, therefore women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately.
• Ability to understand and the willingness to sign an Institutional Review Board (IRB)-approved informed consent document.

Exclusion Criteria:

• Patients who have previously received either gemcitabine or an immune checkpoint inhibitor can be enrolled.
• Emergent need for palliative radiation.
• Patients may not be receiving any other investigational agents for the treatment of nonsmall cell lung cancer.
• History of allergic reaction to gemcitabine.
• Uncontrolled intercurrent illness including, but not limited to ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
• Pregnant women are excluded from this study because of the potential for teratogenic or abortifacient effects with chemotherapy. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with chemotherapy, breastfeeding should be discontinued.