DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed locally advanced or metastatic non-small cell lung cancer

  • Stage IIIB disease that is ineligible for combined modality therapy OR
  • Stage IV disease
• Measurable disease
• No clinically detectable (by physical exam) third-space fluid collection (e.g., ascites or pleural effusions) that cannot be controlled by drainage or other procedures
• No brain metastases (even if treated)

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• ECOG 0-1

Life expectancy:

• At least 12 weeks

Hematopoietic:

• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3
• Hemoglobin at least 9 g/dL

Hepatic:

• Bilirubin no greater than 1.5 times upper limit of normal (ULN)
• AST and ALT no greater than 3 times ULN (5 times ULN if liver metastases present)
• Alkaline phosphatase no greater than 3 times ULN (5 times ULN if liver metastases present)

Renal:

• Creatinine clearance at least 45 mL/min

Other:

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• Able to take folic acid or cyanocobalamin (vitamin B12) supplementation
• No uncontrolled infection
• No concurrent chronic debilitating disease
• No weight loss of 10% or more within the past 6 weeks
• No other prior malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer or noninvasive carcinoma

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• No prior biologic or genetic therapy for lung cancer
• No concurrent immunomodulating agents

Chemotherapy:

• No prior chemotherapy for lung cancer

Endocrine therapy:

• Not specified

Radiotherapy:

• At least 4 weeks since prior radiotherapy to a different site and recovered
• No prior radiotherapy to 25% or more of bone marrow
• No prior radiotherapy to whole pelvis
• No prior radiotherapy for primary disease
• No concurrent radiotherapy

Surgery:

• More than 4 weeks since prior major surgery

Other:

• No aspirin or nonsteroidal anti-inflammatory agents 2 days before, during, and for 2 days after pemetrexed disodium administration (5 days for long-acting agents such as piroxicam, naproxen, diflunisal, or nabumetone)
• No other concurrent cytostatic or cytotoxic therapy