Inclusion Criteria

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