PS-341 in Treating Patients With Metastatic Neuroendocrine Tumors

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