Pemetrexed/Cisplatin Versus Gemcitabine/Cisplatin According to Thymidylate Synthase Expression

Inclusion Criteria: * Histologically confirmed nonsquamous NSCLC * Stage IIIb, IV or recurrent NSCLC * Age ≥ 18years * ECOG performance status of 0 to 1 * Known TS immunohistochemical analysis data * At least one measurable lesion by RECIST 1.1 * No previous chemotherapy or therapy with EGFR TKIs for advanced NSCLC * Asymptomatic brain metastasis or symptomatic brain metastasis treated with local treatment such as operation, whole brain radiotherapy, or gamma-knife surgery * At least 2 weeks later after whole brain radiotherapy or palliative radiotherapy * Adequate renal function: estimated creatinine clearance ≥ 50mL/min Exclusion Criteria: * Patients whose disease recurred within 6 months after the completion of adjuvant chemotherapy. * Patients with post-obstructive pneumonia or uncontrolled serious infection