Testing the Addition of a New Immunotherapy Drug, Atezolizumab (MPDL3280A), to the Usual Chemoradiation (CRT) Therapy Treatment for Limited Stage Small Cell Lung Cancer (LS-SCLC)

Inclusion Criteria:

• Pathologically (histologically or cytologically) proven diagnosis of limited stagesmall cell lung cancer (Stage Tx, T1-T4, N0-3, M0, American Joint Committee onCancer [AJCC] staging, 8th edition [Ed.]), within 60 days prior to registration

• Patients must have received one cycle of platinum/etoposide chemotherapypre-registration (prior to study entry). Study registration must be within 21 daysfrom day 1 of the pre-registration cycle of chemotherapy.

• Patients must have had measurable disease (per Response Evaluation Criteria in SolidTumors [RECIST], version 1.1) prior to the required pre-registration cycle ofplatinum/etoposide chemotherapy

• Minimal staging requirements include:

• History/physical examination within 30 days prior to registration

• Positron emission tomography (PET)/computed tomography (CT) scan for stagingwithin 60 days prior to registration

• CT chest and CT abdomen with IV contrast (unless contraindicated based onkidney function) within 60 days prior to registration; magnetic resonanceimaging (MRI) abdomen with IV contrast allowed in place of CT abdomen

• Note: If contrast allergy exists, premedication per institutionalguidelines should be performed prior to obtaining CT with contrast. Theonly exception to this is a documented life-threatening allergy

• MRI scan of the brain with contrast (preferred) or CT scan of the brain withcontrast (allowable if there is a contraindication with MRI with contrast)within 30 days prior to registration

• Age >= 18

• Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 within 30 daysprior to registration

• Absolute neutrophil count (ANC) >= 1,500/cells/mm^3 (prior to pre-registrationcycle)

• Platelet count >= 100,000 cells/mm^3 (prior to pre-registration cycle)

• Hemoglobin >= 9 g/dL (prior to pre-registration cycle)

• Total bilirubin =< 1.5 x upper limit of normal (ULN) (prior to pre-registrationcycle)

• Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase [SGOT])and alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT]) =< 2.0 x ULN (prior to pre-registration cycle)

• Adequate renal function within 30 days prior to registration defined as follows:Creatinine clearance >= 30 mL/min by the Cockcroft-Gault (C-G) equation

• Patients presenting with a pleural effusion will be eligible if thoracentesis iscytologically negative and non-bloody or if pleural fluid is too small a volume toeffectively sample by thoracentesis and does not show increased metabolic activityon CT/PET imaging

• Negative serum pregnancy test within 14 days of registration for pre-menopausalwomen of childbearing potential

• The patient or a legally authorized representative must provide study-specificinformed consent prior to study entry

• Hepatitis B/C testing prior to enrollment for patients that have not been testedbefore. Note: This is required even if the patient has never shown or had symptomsof hepatitis

• Human immunodeficiency virus (HIV)-infected patients on effective anti-retroviraltherapy with undetectable viral load within 6 months are eligible for this trial

Exclusion Criteria:

• Definitive clinical or radiologic evidence of metastatic disease

• Definitive surgical resection of small cell lung cancer

• Prior invasive malignancy (except non-melanomatous skin cancer, localized prostatecancer, or any early stage cancer treated with curative intent resection) unlessdisease free for a minimum of 2 years (carcinoma in situ of the breast, oral cavity,or cervix are all permissible)

• More than 1 cycle of prior platinum-based chemotherapy for SCLC prior to enrollment;note that prior chemotherapy for a different cancer is allowable

• Any prior atezolizumab or other immunotherapy agent

• Prior radiotherapy to the lungs or mediastinum that would result in clinicallysignificant overlap of radiation therapy fields; prior tangent fields for breastcancer with minimal overlap with target volumes are allowed per approval of studyprincipal investigators (PIs)

• Patients with cytologically positive pleural or pericardial fluid are not eligible

• An active, known or suspected autoimmune disease. Patients are permitted to enrollif they have vitiligo, type I diabetes mellitus, residual hypothyroidism due toautoimmune condition only requiring hormone replacement, psoriasis not requiringsystemic treatment, or conditions not expected to recur in the absence of anexternal trigger

• Active or prior documented inflammatory bowel disease (e.g., Crohn's disease,ulcerative colitis)

• History of allogeneic organ transplant

• History of primary immunodeficiency

• Severe, active co-morbidity defined as follows:

• Known clinically significant liver disease, including active viral, alcoholic,or other hepatitis, cirrhosis, fatty liver, and inherited liver disease

• Any other diseases, metabolic dysfunction, physical examination finding, orclinical laboratory finding giving reasonable suspicion of a disease orcondition that contraindicates the use of an investigational drug or that mayaffect the interpretation of the results or render the patient at high riskfrom treatment complications

• Active tuberculosis

• Active hepatitis B (chronic or acute) or hepatitis C infection. Note that ifhepatitis status is unknown, hepatitis B/C testing is required

• Patients with past or resolved hepatitis B infection (defined as having anegative hepatitis B surface antigen [HBsAg]) test, a positive anti-HBc (antibody to hepatitis B core antigen), and a negative viraldeoxyribonucleic acid (DNA) test (only obtained if HBsAg is foundpositive) are eligible

• Patients positive for hepatitis C virus (HCV) antibody are eligible onlyif polymerase chain reaction (PCR) is negative for HCV ribonucleic acid (RNA). (The HCV RNA test must be performed for patients who have apositive HCV antibody test.)

• Known immunosuppressive disease, for example history of bone marrow transplantor chronic lymphocytic leukemia (CLL)

• Chronic obstructive pulmonary disease (COPD) requiring chronic oral steroidtherapy of > 10 mg prednisone daily or equivalent at the time of registration.Inhaled corticosteroids are not exclusionary

• Unstable angina and/or congestive heart failure requiring hospitalizationwithin the last 3 months

• Transmural myocardial infarction within the last 3 months

• Clinically significant interstitial lung disease

• A condition requiring systemic treatment with either corticosteroids (> 10 mg dailyprednisone equivalents) or other immunosuppressive medications within 14 days ofstudy drug administration. Inhaled or topical steroids and adrenal replacement doses > 10 mg daily prednisone equivalents are permitted in the absence of activeautoimmune disease

• Pregnancy or women of childbearing potential and men who are sexually active and notwilling/able to use medically acceptable forms of contraception for the duration ofstudy treatment and for 150 days after the last dose of study drug (Arm 2); thisexclusion is necessary because the treatment involved in this study may besignificantly teratogenic.