Inclusion Criteria:

          -  Written informed consent including participation in translational research obtained
             from the subject prior to performing any protocol-related procedures, including
             screening evaluations that are not SOC.

          -  ECOG 2

          -  At least one measurable tumor lesion (according to RECIST1.1)

          -  Histologically confirmed small cell lung cancer (SCLC)

          -  Stage IV disease (according to UICC8)

          -  No active autoimmune disease

          -  Adequate organ function defined as:

               -  neutrophil count > 1.5 x 109/L

               -  thrombocytes ≥ 100 x 109/L

               -  hemoglobin ≥ 9 g/dL

               -  INR ≤ 1.4 or aPTT ≤ 40 sec during the last 7 days before therapy [Subjects under
                  therapeutic anticoagulation are permitted.]

               -  bilirubin < 1.5 x ULN

               -  AST (SGOT)/ALT (SGPT) < 3 x institutional ULN (< 5 x ULN in case of liver
                  metastases)

               -  creatinine ≤ 1.5 x ULN or creatinine clearance ≥ 45 mL/min

          -  Availability of tumor tissue/block

          -  Women of childbearing potential (WOCBP) must have a negative serum or urine pregnancy
             test (minimum sensitivity 25 IU/L or equivalent units of HCG) within 72 hours prior to
             the first dose of IMP.

          -  Women of childbearing potential (WOCBP) must use appropriate method(s) of
             contraception. [WOCBP should use an adequate method to avoid pregnancy for 6 months
             after the last dose of IMP.]

          -  Men who are sexually active with WOCBP must use any contraceptive method with a
             failure rate of less than 1% per year. Men receiving IMP and who are sexually active
             with WOCBP will be instructed to adhere to contraception for a period of 6 months
             after the last dose of IMP. Women who are not of childbearing potential (ie, who are
             postmenopausal or surgically sterile) and men who are azoospermic do not require
             contraception.

          -  Subject is willing and able to comply with the protocol for the duration of the study
             including undergoing treatment and scheduled visits and examinations including
             follow-up.

        Exclusion Criteria:

          -  Any preceding systemic anticancer therapy for stage IV SCLC. [Up to one
             full-cycle-dosing of carboplatin+etoposide chemotherapy within the context of SOC is
             permitted prior to study treatment.] (Note: Prior treatment for limited stage disease
             allowed).

          -  Participation in another clinical study with an investigational product during the
             last 30 days before inclusion or 7 half-lives of previously used trial medication,
             whichever is longer

          -  Prior therapy with an anti-Programmed cell death protein 1 (anti-PD-1),
             anti-Programmed cell death-ligand 1 (anti-PD-L1), anti-Programmed cell death-ligand 2
             (anti-PD-L2), anti-CD137 (4-1BB ligand, a member of the Tumor Necrosis Factor Receptor
             [TNFR] family), or anti-Cytotoxic T-lymphocyte-associated antigen-4 (anti-CTLA-4)
             antibody (including ipilimumab or any other antibody or drug specifically targeting
             T-cell co-stimulation or checkpoint pathways).

          -  Previous treatment in the present study (does not include screening failure).

          -  Symptomatic CNS metastases. [Patients with asymptomatic brain metastases may be
             included.]

          -  Major surgery ≤ 28 days before first dose of study treatment

          -  Any uncontrolled systemic disease, condition or comorbidity that, in the opinion of
             the investigator, would interfere with evaluation of study treatment or interpretation
             of patient safety or study results, including but not limited to:

               1. known active HBV, HCV or HIV infection [Patients who are HIV-positive are allowed
                  in the trial, so long as they are stable on anti-retroviral therapy, have a CD4
                  count ≥ 200 cells/μL, and have an undetectable viral load at the time of
                  screening.]

               2. active tuberculosis

               3. any other active infection requiring systemic therapy

               4. history of allogeneic tissue/solid organ transplant

               5. diagnosis of immunodeficiency or patient is receiving chronic systemic steroid
                  therapy or any other form of immunosuppressive therapy within 7 days prior to the
                  first dose of IMP

               6. other active malignancy requiring treatment

               7. clinically significant or symptomatic cardiovascular/cerebrovascular disease
                  (incl. myocardial infarction, unstable angina, symptomatic congestive heart
                  failure, serious uncontrolled cardiac arrhythmia) within 6 months before
                  enrolment

          -  Female subjects who are pregnant, breast-feeding or male/female patients of
             reproductive potential who are not employing an effective method of birth control
             (failure rate of less than 1% per year).

          -  Known hypersensitivity to carboplatin, etoposide or atezolizumab or any of the
             constituents of the product.

          -  Medication that is known to interfere with any of the agents applied in the trial.

          -  Any condition or disease which might interfere with the subject's ability to comply
             with the study procedures (e.g., dementia).

          -  Patient who has been incarcerated or involuntarily institutionalized by court order or
             by the authorities [§ 40 Abs. 1 S. 3 Nr. 4 AMG].

          -  Patients who are unable to consent because they do not understand the nature,
             significance and implications of the clinical trial and therefore cannot form a
             rational intention in the light of the facts [§ 40 Abs. 1 S. 3 Nr. 3a AMG].