The investigators will conduct the randomized trial to determine the role of Gefitinib monotherapy as first-line setting in adenocarcinoma patients with no history of smoking, as compared with the standard combination chemotherapy.

This is a randomized, open label, parallel group, phase III study in never-smokers with advanced or metastatic adenocarcinoma of lung.

After stratification by gender, performance status, and disease stage, patients will be randomized to one of the two treatment arms to receive either gefitinib or standard chemotherapy until clinical or objective disease progression, unacceptable toxicity or patient's refusal, whichever is sooner. The chemotherapy will be administered for no more than nine cycles.

Gefitinib (Iressa TM) Arm - Gefitinib administration 250mg tablet once daily every 3 weeks

standard chemotherapy arm - gemcitabine (1,250mg/m2 for 30 minutes on day 1 and 8 of a 3 week cycle) plus cisplatin (80mg/m2 on day 1 of a 3 week cycle)

Inclusion Criteria:

1. Histologically or cytologically confirmed diagnosis of adenocarcinoma of lung with or without BAC features; however, adenocarcinoma combined with other histology, such as small cell carcinoma or squamous carcinoma, is not allowed.
2. Stage IIIB with malignant pleural effusion/pleural seeding or stage IV patients
3. Age 18-75
4. Never-smoking defined as not more than 100 cigarettes during the lifetime
5. ECOG performance status of 0-2
6. No prior invasive malignancies 5 years prior to study entry except adequately treated cutaneous basal cell carcinoma or uterine cervix in situ cancer
7. Serum creatinine ≤ 1.5 mg/dL, serum bilirubin ≤ 1.2 mg/dL (1 x UNL) and SGOT/SGPT ≤ 100 IU/L (2.5 x UNL)
8. Serum Hgb ≥ 10 gm/dl, platelet count ≥ 100,000/ul, total WBC count >= 4,000/uL, absolute neutrophil count ≥ 1,500/ul
9. Patients must sign an informed consent indicating that they are aware of the investigational nature of the study in keeping with the policy of the hospital. The only approved consent form is attached to this protocol
10. The presence of CNS metastases is not considered as an exclusion criterion, provided that there is good control of the symptoms with corticosteroids

Exclusion Criteria:

1. Pregnancy or breast-feeding (women of child-bearing potential). Women of childbearing potential must practice acceptable methods of birth control to prevent pregnancy.
2. Major surgery other than biopsy within the past two week.
3. Known severe hypersensitivity to Gefitinib or any of the excipients of this product
4. Any evidence of clinically active interstitial lung disease (patients with chronic, stable, radiographic changes who are asymptomatic need not be excluded)
5. As judged by the investigator, any evidence of severe or uncontrolled systemic disease (e.g., unstable or uncompensated respiratory, cardiac, hepatic, or renal disease)
6. Evidence of any other significant clinical disorder or laboratory finding that makes it undesirable for the subject to participate in the study
7. Concomitant use of phenytoin, carbamazepine, rifampicin, barbiturates, or St John's Wort
8. Treatment with a non-approved or investigational drug within 30 days before Day 1 of study treatment.