DISEASE CHARACTERISTICS:

• Pathologically confirmed non-small cell lung cancer (NSCLC)

  • No squamous cell histology
• Stage IIIB (with pleural effusion) or stage IV disease

• Must meet ≥ 1 of the following criteria:

  • Female
  • Adenocarcinoma tumor histology
  • No history of smoking, defined as smoking < 100 cigarettes (5 standard packs of cigarettes) in a lifetime, < 20 oz of pipe tobacco in a lifetime, OR < 100 cigars in a lifetime
  • Asian/Pacific Rim ethnicity, defined as Japanese, Chinese, Korean, or other Asian/Pacific Rim ethnicity
• Must have activating mutations in the TK region of the epidermal growth factor receptor (EGFR) gene
• Measurable disease

• No symptomatic or newly diagnosed CNS metastases that have not been definitively treated with radiotherapy and/or surgery

  • History of CNS metastases or cord compression allowed if definitively treated and clinically stable

PATIENT CHARACTERISTICS:

• See Disease Characteristics
• ECOG performance status 0-2
• Life expectancy ≥ 12 weeks
• Absolute neutrophil count ≥ 2,000/mm³
• Platelet count ≥ 100,000/mm³
• Bilirubin ≤ 1.25 times upper limit of normal (ULN)
• ALT and AST ≤ 2.5 times ULN (5 times ULN if liver has tumor involvement)
• Creatinine ≤ 1.5 times ULN OR creatinine clearance ≥ 60 mL/min
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No known severe hypersensitivity to gefitinib or any other component of gefitinib tablets

• No evidence of clinically active interstitial lung disease

  • Patients with chronic, stable radiographic changes who are asymptomatic are eligible
• No other concurrent malignancy or malignancy diagnosed within the past 5 years except for basal cell carcinoma of the skin or cervical cancer in situ
• No concurrent severe or uncontrolled systemic disorder
• No evidence of any other significant clinical disorder or laboratory finding that, in the opinion of the investigator, would preclude study participation
• Able to tolerate protocol treatment, in the opinion of the investigator

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• No prior systemic chemotherapy, biological therapy, immunotherapy, or hormonal therapy for NSCLC, including adjuvant and neoadjuvant treatment

• No prior radiotherapy to the target lesion

  • Prior radiotherapy to bony disease or CNS disease allowed
• At least 2 weeks since prior radiotherapy and recovered
• More than 30 days since prior non-FDA approved or investigational agents
• No prior EGFR antagonists
• At least 2 weeks since prior and no concurrent phenytoin, carbamazepine, rifampin, barbiturates, or Hypericum perforatum (St. John's wort)
• No concurrent chemotherapy, immunotherapy, hormonal therapy, nonpalliative radiotherapy, surgery for cancer, or other experimental medications
• No other concurrent specific antitumor therapy