Inclusion Criteria:

          -  Age >= 18 years of age

          -  Have an Eastern Cooperative Oncology Group (ECOG) performance status of =< 1 at the
             time of study treatment initiation

          -  Histologically or cytologically confirmed diagnosis of small cell lung cancer (SCLC)

          -  Patient should have extensive stage disease, defined as, malignant pleural effusion,
             pulmonary metastases in a different lobe in the ipsilateral lung or contralateral
             lung, and/or the presence of extra-thoracic metastatic disease

          -  Must have measurable disease based on Response Evaluation Criteria in Solid Tumors
             (RECIST) 1.1 prior to starting platinum-based systemic chemotherapy

          -  Absolute neutrophil count (ANC) >= 1.5 x 10^9/L

          -  Platelets >= 100 x 10^9/L

          -  Hemoglobin >= 9 g/dL

          -  Serum creatinine =< 1.5 x institution upper limit of normal (ULN) and calculated
             creatinine clearance of at least 15 ml/min

          -  Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) =< 3 x upper limit
             of normal (ULN) (ALT and AST =< 5 x ULN is acceptable if liver metastases are present)

          -  Total serum bilirubin =< 1.5 x ULN. For patients with well documented Gilbert's
             syndrome, total bilirubin =< 3 x ULN with direct bilirubin within normal range

          -  Newly diagnosed SCLC patients may receive no more than 1 cycle of standard
             chemotherapy or chemoimmunotherapy for their current diagnosis prior to study
             treatment

          -  Patients who have progressed on prior treatment for SCLC will be eligible if both of
             the following conditions are met:

               -  Received no more than one-line of treatment with platinum-based chemotherapy for
                  SCLC, and

               -  Last platinum-based treatment administered >= 12 months prior to diagnosis of
                  recurrence/relapse. Patients should not have experienced disease progression
                  while receiving prior platinum-based treatment for SCLC

          -  Participants of child-bearing potential must agree to use adequate contraceptive
             methods (e.g., hormonal or barrier method of birth control; abstinence) prior to study
             entry. Should a woman become pregnant or suspect she is pregnant while she or her
             partner is participating in this study, she should inform her treating physician
             immediately

          -  Participant or legal representative must understand the investigational nature of this
             study and sign an approved written informed consent form prior to receiving any study
             related procedure

        Exclusion Criteria:

          -  Receipt of anticancer chemotherapy/chemoimmunotherapy within 4 weeks prior to the
             first administration of study drug other than what is allowed in the inclusion
             criteria

          -  Symptomatic brain metastasis

               -  Patients with treated brain metastases are eligible provided they have recovered
                  from effects of radiation and neurological symptoms are improved or controlled
                  for at least two weeks prior to enrollment

               -  Patients with asymptomatic brain metastases who are being treated with systemic
                  chemotherapy alone are also eligible if no more than 6 lesions each less than 1
                  cm in size is present at the time of initiating protocol treatment

          -  Leptomeningeal involvement regardless of treatment status

          -  Participation in another interventional study within the last 28 days of study
             enrollment

          -  Had major surgery within 14 days prior to starting study drug or has not recovered
             from major side effects (tumor biopsy is not considered major surgery) resulting from
             a prior surgery

          -  Positive for immunosuppressive disease, acquired immunodeficiency syndrome (AIDS) or
             other immune depressing diseases. For human immunodeficiency virus (HIV), HVC and
             HBC-mandatory testing is required prior to enrollment

               -  Note: Patients with past or resolved hepatitis B virus (HBV) infection (defined
                  as the presence of hepatitis B surface antibody [HBsAb] and absence of hepatitis
                  B surface antigen [HBsAg]) are eligible (HBV deoxyribonucleic acid [DNA] should
                  be obtained in patients if only anti-hepatitis B core [HBc] antibody was present
                  prior to randomization). Patients with active/untreated hepatitis C virus (HCV)
                  will be excluded from the study; patients who test positive for HCV antibody are
                  eligible only if polymerase chain reaction (PCR) is negative for HCV ribonucleic
                  acid (RNA)

          -  Active, clinically serious infections or other serious uncontrolled medical
             conditions, including chronic viral hepatitis (testing for hepatitis B, C required)

          -  Patient has known hypersensitivity to the components of the study drugs or any analogs

          -  History or current evidence of any condition, therapy, or laboratory abnormality that
             might confound the results of the study, interfere with the patient's participation
             for the full duration of the study, or is not in the best interest of the patient to
             participate, in the opinion of the treating Investigator, including, but not limited
             to:

               -  Myocardial infarction or arterial or venous thromboembolic events within 6 months
                  prior to baseline or severe or unstable angina, New York Heart Association (NYHA)
                  class III or IV disease

               -  History of documented congestive heart failure (New York Heart Association
                  functional classification III or IV) within 6 months prior to baseline

               -  Poorly controlled arrhythmias

          -  Contraindications to atezolizumab: Patients with active autoimmune disorder or prior
             history of autoimmune disorder requiring immunosuppressive agents within preceding two
             years will not be allowed to receive atezolizumab but will be able to receive the
             other drugs included in the treatment regimen, if eligible