Bortezomib in Treating Patients With Unresectable or Metastatic Gastric Cancer or Gastroesophageal Junction Adenocarcinoma

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed unresectable or metastatic gastric or gastroesophageal junction adenocarcinoma Siewert's class II or III disease Measurable disease At least 1 unidimensionally measurable lesion at least 20 mm by conventional techniques OR at least 10 mm by spiral CT scan No history of known or active brain metastases or primary brain tumors PATIENT CHARACTERISTICS: Age 18 and over Performance status Karnofsky 60-100% OR ECOG 0-2 Life expectancy Not specified Hematopoietic WBC at least 3,000/mm^3 Absolute neutrophil count at least 1,000/mm^3 Platelet count at least 100,000/mm^3 Hepatic Bilirubin no greater than 1.5 mg/dL AST and ALT no greater than 3 times upper limit of normal (ULN) (5 times ULN if liver metastases are present) Renal Creatinine no greater than 1.5 mg/dL Cardiovascular No prior cerebrovascular event No prior orthostatic hypotension No myocardial infarction within the past 6 months No peripheral vascular disease requiring surgical management No evidence of acute ischemia or significant conduction abnormality by EKG Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for at least 2 months after study participation No evidence of peripheral neuropathy No prior allergic reaction attributed to compounds of similar chemical or biological composition to bortezomib No other malignancy within the past 3 years except basal cell skin cancer, carcinoma in situ of the cervix, or adequately treated nonmetastatic prostate cancer No ongoing or active infection No psychiatric illness or social situation that would preclude study participation No other concurrent uncontrolled illness that would preclude study participation No other medical condition or reason that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy More than 3 weeks since prior immunotherapy No concurrent biological or immunological agents Chemotherapy No more than 1 prior chemotherapy regimen (including adjuvant chemotherapy) More than 3 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) No concurrent chemotherapy Endocrine therapy Not specified Radiotherapy More than 3 weeks since prior radiotherapy No concurrent radiotherapy Surgery Not specified Other Recovered from all prior therapy No other concurrent investigational agents No other concurrent anticancer agent or therapy