A Phase II Study of 131I- Metaiodobenzylguanidine (MIBG) for Treatment of Metastatic or Unresectable Pheochromocytoma and Related Tumors

Inclusion Criteria: * Histologic Documentation: Histologic documentation of malignant pheochromocytoma or related tumors (paraganglioma, neuroblastoma, medullary thyroid carcinoma, carcinoid tumors), not amenable to curative surgery. Any site of origin of malignant pheochromocytoma, including but not limited to: adrenal, neck, thorax, abdominal, or pelvis is allowed. * Prior Treatment: * No cytotoxic chemotherapy for at least 3 weeks prior to high-dose 131I-MIBG or concurrent with high-dose 131I-MIBG. * \> 2 weeks since major surgery. * \> 4 weeks since completion of prior radiation therapy, as long as measurable disease lies outside the radiation port. * No treatment with an investigational agent concurrent or within 30 days of high-dose 131I-MIBG. * Patients who have received previous chemotherapy or radiation therapy must have evidence of persistent disease on 123I-MIBG scan and elevated tumor markers or measurable CT lesions before receiving high-dose 131I-MIBG. * Metastases Excluding Eligibility: No patients with a known significant MIBG-avid parenchymal brain metastasis; leptomeningeal metastases do not exclude eligibility. Hepatic metastases exclude eligibility if they functionally impair liver function (AST or total bilirubin ≥ 2.5 times the ULN). * Measurable Disease Lesions that can be accurately measured in at least one dimension (longest diameter to be recorded) as \> 10 mm as measured with CT scanning. Lesions \< 10 mm diameter or bone lesions in the presence of demonstrable uptake of 123I-MIBG on diagnostic scanning, plus elevated levels of tumor markers that are specific for malignant pheochromocytoma: plasma catecholamines or metanephrines, urine catecholamines or metanephrines, serum chromogranin A. Lesions whose size is considered non-measurable include the following: * Bone lesions (see above) * Leptomeningeal disease * Ascites * Pleural/pericardial effusion * Chylothorax * Lesions within the chest or abdomen that are not confirmed to be pheochromocytoma by biopsy or 123I-MIBG scanning. * 131I-MIBG or 123I-MIBG Avidity: All patients must have 123I-MIBG or 131I-MIBG whole-body scanning prior to therapy. Metastases must be avid for the isotope such that their measured gamma radiation measures ≥ twice that of background radiation. * Subsequent 131I-MIBG Therapies: Patients must have had pain relief or a SD or PR after a prior therapy to be eligible for another therapy. Patients with PD within 9 months of the prior therapy are excluded from receiving subsequent therapy. * Age: ≥4 years of age. * Life Expectancy: greater than 9 months. * Karnofsky Performance Status: 70% or higher. * Anticoagulation: Heparin, LMW heparin, coumadin, and other anticoagulants may be used only when platelet counts are ≥ 100,000/micronL. Platelet counts will be monitored twice weekly after 131I-MIBG therapy. * Pregnancy \& Nursing: Non-pregnant and non-nursing because the effects of high-dose 131I-MIBG on the fetus/infant are unknown. * Second Malignancies: * Patients with a "currently active" second malignancy, other than non-melanoma skin cancers, are not eligible. * Patients are not considered to have a "currently active" second malignancy if they have been cancer-free for ≥5 years. * Intercurrent Illness: No patients with uncontrolled intercurrent illness including but not limited to: ongoing active infections, grade 3 or 4 congestive heart failure by echocardiogram, nephrotic syndrome, serum albumin \< 3, significant ascites or pleural effusion, pulmonary function testing (FVC) less than 70% of predicted for age, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements * Required Initial Laboratory Data (Minimum Levels): * Neutrophil count \>/= 1,000/micronL * Platelet count \>/= 80,000/micronL * AST (SGOT) ≤ 2.5 x ULN * Total bilirubin ≤ 2.5 x ULN * Creatinine ≤ 2 x ULN Exclusion Criteria: * 1\) Pregnancy \& Nursing: Non-pregnant and non-nursing because the effects of high-dose 131I-MIBG on the fetus/infant are unknown. * 2\) Second Malignancies: * Patients with a "currently active" second malignancy, other than non-melanoma skin cancers, are not eligible. * Patients are not considered to have a "currently active" second malignancy if they have been cancer-free for ≥5 years * 3\) Intercurrent Illness: No patients with uncontrolled intercurrent illness including but not limited to: ongoing active infections, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.