Limited Stage Small Cell Lung Cancer (LS-SCLC): A Phase III Randomized Study of Chemoradiation Versus Chemoradiation Plus Atezolizumab

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

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

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

• Minimal staging requirements include:

‣ History/physical examination within 30 days prior to registration

⁃ Positron emission tomography (PET)/computed tomography (CT) scan for staging within 60 days prior to registration

⁃ CT chest and CT abdomen with IV contrast (unless contraindicated based on kidney function) within 60 days prior to registration; magnetic resonance imaging (MRI) abdomen with IV contrast allowed in place of CT abdomen

∙ Note: If contrast allergy exists, premedication per institutional guidelines should be performed prior to obtaining CT with contrast. The only exception to this is a documented life-threatening allergy

⁃ MRI scan of the brain with contrast (preferred) or CT scan of the brain with contrast (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 days prior to registration

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

• 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-registration cycle)

• 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 is cytologically negative and non-bloody or if pleural fluid is too small a volume to effectively sample by thoracentesis and does not show increased metabolic activity on CT/PET imaging

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

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

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

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