This study is a single-center, randomized controlled, phase II clinical trial, aiming at giving a comparison of Sintilimab and Pembrolizumab in stage IIIB-IV NSCLC patients at first-line treatment setting.

This trial has been set up with two arms. Screened patients would be included into one of the arms based on tumor PD-L1 expression. The purpose of this study is to compare the efficacy of the approved checkpoint inhibitor pembrolizumab and home-made drug Sintilimab in patients with advanced NSCLC whose tumor have high PD-L1 expression and low or negative expression.

Inclusion Criteria:

1. Age≥18 years. Signed Informed Consent Form.
2. Stage IV NSCLC confirmed by histology/ cytology or Stage IIIB-IIIC NSCLC that could not be treated with radical radiation therapy (8th edition of IASLC Lung Cancer Staging System).
3. Fresh tumor tissue or paraffin tissue within 6 months is adequate for PD-L1 expression (TPS) testing in the central laboratory.
4. Tumor tissue without EGFR mutation or ALK rearrangement must be confirmed.
5. Per RECIST 1.1 the efficacy evaluation criteria for solid tumors, at least one radiologically measurable lesion which was not treated with radiotherapy or had obvious disease progression after radiotherapy.
6. Patients who received no systemic chemotherapy or any other systemic treatment for advanced NSCLC. For patients who received preoperative neoadjuvant chemotherapy or postoperative adjuvant chemotherapy or radical chemoradiotherapy, if the disease progresses occurred one six months after the last treatment, they can be enrolled. Patients who received targeted therapy or immunotherapy can not be enrolled.

Exclusion Criteria:

1. Active hepatitis B. Active hepatitis B is defined as HBsAg positive and the detected HBV-DNA copy number is larger than the upper limit of normal value in the laboratory of the study site.
2. Currently or prior clinically active interstitial lung disease. Currently active pneumonia. Current radiation pneumonitis for which corticosteroid treatment is required.
3. Known HIV antibody positive, or other acquired or congenital immunodeficiency diseases, or history of organ transplantation.
4. Fever and the body temperature is above 38°C or clinically significant infection within 1 week prior to the enrollment.
5. Active tuberculosis. Evidence of severe or uncontrollable systemic diseases (such as severe mental, neurological diseases, seizure, or dementia, unstable or non-compensatory respiratory, cardiovascular, hepatic or renal diseases, and uncontrolled hypertension [CTCAE Grade 2 hypertension or above after drug treatment]).
6. Patients with active bleeding or new thrombotic diseases who are orally taking with anticoagulant drugs or have bleeding tendency.