DISEASE CHARACTERISTICS:

• One of the following histologically or cytologically confirmed cancers not amenable to treatment with combined chemotherapy and radiotherapy:

  • Biliary tract (intrahepatic, extrahepatic, or ampulla of Vater) carcinoma
  • Gallbladder carcinoma
• Unresectable or metastatic disease

• No CNS metastases

  • Prior brain metastases treated with surgery or radiosurgery allowed provided treatment was completed at least 4 weeks ago and there is no evidence of CNS progression
• No clinically significant pericardial or pleural effusion or ascites unless able to be drained before study entry

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• ECOG 0-2

Life expectancy

• At least 3 months

Hematopoietic

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

Hepatic

• Bilirubin no greater than 3 times upper limit of normal (ULN)
• AST no greater than 5 times ULN

Renal

• Creatinine no greater than 1.5 times ULN OR
• Creatinine clearance at least 45 mL/min

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer
• Able to tolerate folic acid, corticosteroids, or cyanocobalamin supplements

PRIOR CONCURRENT THERAPY:

Biologic therapy

• More than 4 weeks since prior biologic or immunologic therapy
• No prior biologic or immunologic therapy for metastatic disease
• No concurrent immunotherapy
• No concurrent colony-stimulating factors during course 1

Chemotherapy

• No prior chemotherapy for metastatic disease
• No prior gemcitabine

• Prior chemoembolization allowed provided the following are true:

  • At least 4 weeks since prior chemoembolization
  • Evidence of new tumor growth since therapy
• At least 6 months since prior chemotherapy used as a radiosensitizer (in adjuvant setting or for locally advanced disease)
• No other concurrent chemotherapy

Endocrine therapy

• Not specified

Radiotherapy

• Prior radiofrequency ablation allowed provided the following are true:

  • At least 4 weeks since prior radiofrequency ablation
  • Evidence of new tumor growth since therapy
• No prior radiotherapy to 25% or more of the bone marrow
• More than 4 weeks since prior radiotherapy
• No concurrent radiotherapy

Surgery

• Not specified

Other

• Prior embolization allowed provided the following are true:

  • At least 4 weeks since prior embolization
  • Evidence of new tumor growth since therapy
• No prior pemetrexed disodium
• No aspirin or nonsteroidal anti-inflammatory drugs for at least 2 days (5 days for long-acting agents [e.g., piroxicam]) before, during, and for at least 2 days after administration of pemetrexed disodium
• No concurrent cyclo-oxygenase-2 inhibitors