This study is for people with advanced gastric or gastroesophageal cancer. This study is being done to find out how long it takes tumors to grow after receiving treatment with the drugs irinotecan (also known as CPT-11) and docetaxel (also known as Taxotere). Irinotecan is a drug that has been approved by the Food and Drug Administration (FDA). Irinotecan has been approved for treatment of cancer of the colon and rectum. Docetaxel is another drug approved by the FDA. Docetaxel is approved for treatment of breast, prostate and lung cancer. However, the FDA has authorized the use of irinotecan and docetaxel in this study. This study will evaluate the effects of these drugs on participant's tumors. The side effects of the combination of irinotecan and docetaxel will also be evaluated. This study will also measure the levels of certain substances in participant's tumors. These substances, called genes (which are the cell's blueprint), affect how people's bodies react to the cancer drugs. Genes will also be measured in participant's blood. The researchers want to see if these substances can predict response to the study drugs.

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.