Capecitabine and Streptozocin With or Without Cisplatin in Treating Patients With Unresectable or Metastatic Neuroendocrine Tumors

DISEASE CHARACTERISTICS: * Histologically confirmed unresectable, advanced, and/or metastatic disease meeting one of the following types: * Gastroentero-neuroendocrine tumor of the foregut * Pancreatic neuroendocrine tumor * Neuroendocrine tumor of unknown primary * Measurable disease, defined as at least 1 lesion that can be accurately measured in at least 1 dimension (the longest diameter) ≥ 20 mm by conventional CT scanning or ≥ 10 mm by spiral CT scan or MRI * No bronchial neuroendocrine tumors (NETs) or other NETs where the primary site is situated in organs above the diaphragm (e.g., laryngeal and pharyngeal NETs) PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Life expectancy ≥ 12 weeks * Hemoglobin ≥ 10 g/dL * Platelet count ≥ 100,000/mm³ * WBC ≥ 3,000/mm³ * ANC ≥ 1,500/mm³ * Bilirubin ≤ 2 times upper limit of normal (ULN) * Alkaline phosphatase ≤ 5 times ULN * AST and ALT ≤ 5 times ULN * GFR ≥ 60 mL/min * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 3 months after completion of study therapy * No other serious or uncontrolled illness that would preclude study participation * No medical or psychiatric condition that would influence the ability to provide consent PRIOR CONCURRENT THERAPY: * At least 3 weeks since prior interferon therapy * No prior systemic chemotherapy or chemotherapy administered as part of a chemo-embolization regimen, or for this condition * No receptor-tar…