Bortezomib With or Without Irinotecan in Treating Patients With Cancer of the Gastroesophageal Junction or Stomach

This phase II trial is studying how well bortezomib with or without irinotecan works in treating patients with gastroesophageal junction or stomach cancer that can not be removed by surgery. Bortezomib may stop the growth of tumor cells by blocking the enzymes necessary for tumor cell growth. Drugs used in chemotherapy such as irinotecan use different ways to stop tumor cells from dividing so they stop growing or die. Combining bortezomib with irinotecan may kill more tumor cells.