Inclusion Criteria:

          -  Age ≥18 years

          -  Signed written informed consent

          -  Histologically or cytological diagnosed stage IIIB/IV non-squamous histology NSCLC

          -  Received platinum based doublet chemotherapy for 4 cycles as first line therapy before
             this study

          -  Patients upon enrolment has at least stable disease following the platinum doublet;
             with documented (confirmed or unconfirmed) radiographic evidence of a tumor response
             of complete response (CR), partial response (PR), or stable disease (SD) according to
             RECIST version 1.1 criteria

          -  Estimated Life expectancy ≥ 3 months

          -  Eastern cooperative oncology group performance status (ECOG PS) 0-2

          -  Adequate organ function

        Exclusion Criteria:

          -  Age ˂18 years

          -  Predominantly squamous cell and/or mixed small cell, non-small cell histology

          -  Current treatment on another therapeutic clinical study or within the last 30 days of
             entering the study

          -  Spinal cord compression unless treated with the patient attaining good pain control
             and stable or recovered neurologic function, carcinomatous meningitis, or
             leptomeningeal disease

          -  Any of the following within the 3 months prior to starting study treatment: myocardial
             infarction, severe/unstable angina, coronary/peripheral artery bypass graft,
             congestive heart failure, or cerebrovascular accident including transient ischemic
             attack

          -  Ongoing cardiac dysrhythmias of national cancer institute-common terminology criteria
             for adverse events (NCI CTCAE) Grade >2, uncontrolled atrial fibrillation of any
             grade, or corrected QT interval (QTc) >470 msec

          -  Pregnancy or breastfeeding

          -  Prior malignancy (other than current NSCLC): patients will not be eligible if they
             have evidence of active malignancy (other than non-melanoma skin cancer or localized
             cervical cancer, or localized and presumed cured prostate cancer) within the last 3
             years

          -  Other severe acute or chronic medical or psychiatric conditions, or laboratory
             abnormalities that would impose, in the judgment of the investigator and/or sponsor,
             excessive risk associated with study participation or study drug administration, and
             which would, therefore, make the patient inappropriate to enter this study

          -  Uncontrolled third-space fluid collections

          -  Progressive brain metastases

          -  Hypersensitivity to the study drugs

          -  Inability to take corticosteroid drugs, folic acid, or vitamin B12

          -  Patients with epidermal growth factor receptor (EGFR) positive, anaplastic lymphoma
             kinase (ALK) positive (documented using fluorescence in situ hybridization (FISH)
             and/or immunohistochemistry (IHC)), or unknown EGFR and ALK test results