Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed metastatic carcinoid tumor or islet cell tumor

- Well-differentiated neuroendocrine tumor OR

- Well-differentiated neuroendocrine carcinoma

- Measurable disease in at least 1 dimension

- At least 20 mm by conventional techniques OR at least 10 mm by spiral CT scan

- The following are considered nonmeasurable:

- Lesions in a previously irradiated area

- Bone lesions

- Leptomeningeal disease

- Ascites

- Pleural/pericardial effusion

- Lymphangitis cutis/pulmonis

- Abdominal masses that are not confirmed and followed

- Cystic lesions

PATIENT CHARACTERISTICS:

Age:

- 18 and over

Performance status:

- ECOG 0-2

Life expectancy:

- At least 6 months

Hematopoietic:

- Leukocyte count at least 3,000/mm^3

- Absolute neutrophil count at least 1,500/mm^3

- Platelet count at least 100,000/mm^3

Hepatic:

- Bilirubin no greater than 1.5 mg/dL

- AST/ALT no greater than 2.5 times upper limit of normal

Renal:

- Creatinine no greater than 1.5 mg/dL

Cardiovascular:

- No symptomatic congestive heart failure

- No unstable angina pectoris

- No cardiac arrhythmia

Other:

- No other uncontrolled illness

- No ongoing active infection

- No psychiatric illness or social situation that would preclude study

- No history of allergic reaction to compounds of similar chemical or biologic
composition to bortezomib

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- At least 4 weeks since prior immunotherapy (interferon alfa)

Chemotherapy:

- No more than 1 prior systemic chemotherapy regimen (except hepatic artery
chemoembolization)

- At least 4 weeks since prior systemic chemotherapy (6 weeks for nitrosoureas)

- At least 12 weeks since prior hepatic artery chemoembolization (unless liver lesions
are not indicator lesions)

- Stable dose long-acting octreotide therapy (Sandostatin LAR) within the past 3 months
allowed

- Concurrent subcutaneous octreotide for breakthrough symptomatic relief allowed

Endocrine therapy:

- Not specified

Radiotherapy:

- See Disease Characteristics

- At least 4 weeks since prior radiotherapy

Surgery:

- Not specified

Other:

- No other concurrent investigational agents, commercial agents, or therapies

- No concurrent combination antiretroviral therapy for HIV-positive patients