A Study of Concurrent Chemoradiation With Atezolizumab in Participants With Untreated Extensive-Stage (ES) Small Cell Lung Cancer (SCLC)

participants receive EC/EP chemotherapy combined with Atezolizumab for 2 cycles, and the efficacy will be evaluated. If the efficacy evaluation is SD/PR/CR, concurrent chemoradiotherapy comined with EC/EP(2 cycles) +Atezolizumab will be initiated. After concurrent chemoradiotherapy +Atezolizumab, Atezolizumab was maintained until PD or intolerance or for at most 2 years.

participants with brain metastases will receive radiotherapy for brain metastases during the first 2 cycles of chemotherapy.

Inclusion criteria

1.Histologically confirmed ES-SCLC (per the Veterans Administration Lung Study Group [VALG] staging system) 2.Must sign a written informed consent form prior to any study specific procedures 3. No prior treatment for ES-SCLC 4.Measurable disease, as defined by RECIST v1.1 5.Can tolerate radiotherapy, no contraindication of radiotherapy 6.Weight≥40kg 7.Life expectancy>12 weeks 8. Eastern Cooperative Oncology Group (ECOG) performance status of 0 - 1. 9.Systemic immunosuppressive doses of corticosteroids (prednisone>10 mg/d or equivalent) was discontinued at least 2 weeks before registration for protocol therapy.

• Be willing to provide 20 tissue sections(4-6 micron thickness) from a newly obtained core or excisional biopsy of a tumor lesion, for biomarker exploration; newly-obtained is defined as a specimen obtained within 3 months before initiation of treatment on day 1; newly-obtained samples must be core needle biopsy, excision, or incision 11.Must have adequate organ function defined by the following laboratory results:

• Absolute neutrophil count (ANC) ≥ 1.5×109/L, Platelets≥ 100×109/L, Hemoglobin≥90g/L
• Serum creatinine ≤ 1.5 upper limit of normal (ULN) OR calculated creatinine clearance≥60 mL/min(using Cock-Gault formula)
• Total bilirubin ≤1.5 ULN or for total bilirubin level ≥1.5 ULN, direct bilirubin is within normal limits; AST (SGOT) and ALT (SGPT)≤2.5 ULN.
• The thyroid-stimulating hormone (TSH) is within normal range. Note: If the Baseline TSH is not within the normal range, and T3 and T4 are within the normal range, the subject may still meet the inclusion criteria.
• International normalized ratio(INR) or prothrombin time(PT), activated partial thromboplastin time (APTT)≤1.5 ULN, exception: In subjects receiving anticoagulant therapy, as long as PT or APTT is within the recommended use of anticoagulants
• Baseline ECG showed no prolonged PR interval or atrioventricular block. 12.Women of child-bearing potential should agree that contraception (such as intrauterine devices(LUD), birth control pills or condoms) must be used during the course of the study through 6 months after the last dose of study medication, and women of childbearing potential should have a negative urine or serum pregnancy test within 7 days prior to receiving the first dose of study medication and must be a non-lactation participant; the male participants agree to use contraception during the study period and for 6 months after the end of the study period.

Exclusion criteria

• Hypersensitivity to Atezolizumab
• Carcinomatous meningitis.
• History of active Bacillus tuberculosis (TB)
• Active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs); replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment
• HIV positive or with Acquired Immune Deficiency Syndrome
• Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy
• History of, or any evidence of active, non-infectious pneumonitis
• Immunosuppressive drug was used 2 weeks prior to the first study drug treatment, excluding topical glucocorticoid, systematic glucocorticoid not exceeding 10 mg/d of prednisone or equivalent dose of other glucocorticoid
• Received a live vaccine within 30 days of planned start of study therapy
• Received a prior anti-cancer monoclonal antibody (mAb) within 3 months prior to study day 1
• Has taken Chinese herbal medicine for anti-cancer purpose in the past 2 weeks
• Known active hepatitis B (e.g., hepatitis B virus surface antigen [HBsAg] reactive) or hepatitis C (HCV) (e.g., HCV ribonucleic acid [RNA] [qualitative] is detected)
• Active infection requiring systemic therapy
• Known additional malignancy that is progressing or requires active treatment; exceptions include basal cell carcinoma of the skin or squamous cell carcinoma of the skin that has undergone potentially curative therapy or in situ cervical cancer
• Bleeding tendency, such as active peptic ulcer, or treated with anticoagulants or vitamin K antagonists, such as Warfarin, Heparin, or their analogues
• Any severe and/or uncontrolled disease, such as: (1) unstable angina pectoris, symptomatic congestive heart failure, myocardial infarction within 6 months prior to randomization, severe uncontrolled arrhythmia; poor blood pressure control (SBP>140 mmHg, DBP>90 mmHg) ; (2)active or uncontrolled severe infection; (3)liver diseases such as cirrhosis, decompensated liver disease, chronic active hepatitis; (4) poor control of diabetes (FBG>10mmol/l) ; (5) urine routine suggested urinary protein ≥ + + and 24-hour urinary protein quantitation >1.0 g; (6) history of psychotropic substance abuse and could not be cured or had mental disorder
• Prisoner who is imprisoned or forcibly detained for reasons other than mental or physical (e.g. infectious) disease
• Can not tolerate venipuncture
• Pregnant or lactating women
• Other conditions that researchers consider unsuitable for participation -