Study of Irinotecan and Docetaxel in Patients With Metastatic or Unresectable Gastric or Gastroesophageal Junction Adenocarcinoma

Inclusion Criteria: * Patients must have clinically documented unresectable or metastatic gastric cancer or gastroesophageal adenocarcinoma and histologic confirmation of the diagnosis with tumor. * Patients must have received one prior chemotherapeutic regimen for metastatic or unresectable disease. Patients may not have received prior therapy with irinotecan or a taxane. * Tissue from tumor must be available. This may be paraffin embedded tissue from previous biopsy/resection or if it is not available, a repeat biopsy must be performed. * Patients must agree to have a 20 cc blood sample drawn in addition to routine labs with each cycle of chemotherapy. * Patients must have measurable disease by clinical exam or radiologic studies, that is at least one lesion measurable in at least one dimension, measuring 10 mm or more on a spiral CT scan, or at least 20 mm by an exam or a non-spiral scan. If prior radiation therapy was administered, measurable disease must be outside the radiation field. * Patients must have a Zubrod performance status of 0-2. * Patients must have a predicted life expectancy of at least 12 weeks. * Patients must have: * a pre-treatment granulocyte count (i.e., segmented neutrophils + bands) of \>1,500/mm3, * a hemoglobin level of greater than or equal to 9.0 gm/dl, and * a platelet count of \>100,000/mm3. * Patients must have adequate renal function as documented by a calculated creatinine clearance \> 60. * Patients must have adequate hepatic function as documented by a serum bilirubin less than or equal to the institutional upper limit of normal, regardless of whether patients have liver involvement secondary to tumor. * No major surgery within 1 month of starting study drug. * Women of childbearing potential must have a negative pregnancy test. * Peripheral neuropathy: must be \< grade 1 Exclusion Criteria: * Patients may not have a history of an allergy to irinotecan. * Patients with any active or uncontrolled infection, including known HIV infection. * Patients with psychiatric disorders that would interfere with consent or follow-up. * Patients with a history of myocardial infarction within the previous six months or congestive heart failure requiring therapy. * Pregnant or lactating women. Men and women of reproductive potential may not participate unless they have agreed to use an effective contraceptive method while on treatment and for at least 3 months thereafter. * Presence of clinically apparent central nervous system metastases or carcinomatous meningitis. * Patients with a history of seizures are ineligible. Patients receiving phenytoin, phenobarbital, or other anti-epileptic prophylaxis are ineligible. * Patients with any other severe concurrent disease, which in the judgment of the investigator would make the patient inappropriate for entry into this study. * Patients with a history of severe hypersensitivity reaction to docetaxel or other drugs formulated with polysorbate 80.