Inclusion Criteria

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