This study trys to evaluate the predictive role of thymidylate synthase expression for pemetrexed/cisplatin in Non-small Cell Lung Cancer (NSCLC).

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