• To determine and quantify tumor uptake of radiolabeled antibody from measurements with: [ Time Frame: Until end of study ] [ Designated as safety issue: No ]
  
• PET imaging/Dosimetry [ Time Frame: Until end of study ] [ Designated as safety issue: No ]
  
• Autoradiographs - tumor or biopsy samples [ Time Frame: Until end of study ] [ Designated as safety issue: No ]
  
• Ex vivo radioactivity estimates - tumor, normal tissue and serum samples [ Time Frame: Until end of study ] [ Designated as safety issue: No ]
  
• Toxicity defined by NCI Common Toxicity Criteria [ Time Frame: Until end of study ] [ Designated as safety issue: Yes ]
  

• Serum radioactivity, volume of distribution, and half-life following IV and IA 124I-huA33 [ Time Frame: Until end of study ] [ Designated as safety issue: No ]
  
• HAHA levels - measured by plasmon resonance surface (Biacore®) assay [ Time Frame: Until end of study ] [ Designated as safety issue: No ]
  

Drug: Iodine-124 labeled humanized A33 (antibody)
Patients will receive a single intravenous or intraarterial infusion of 10mg huA33, labeled with 4mCi-10mCi of 124I in 5-30ml of 5% HSA in normal saline (NS), over 5-10 minutes. On study days 2, 3, and/or 4 patients will have the option to receive up to 2g/kg of IVIG. Patients will be evaluated with 124I-huA33 positron-emission tomography (PET) with ex vivo quantitation of tumor uptake.

This is an open-label, pilot study of a single 4mCi-10mCi/10mg IV dose of 124I-huA33 in patients with colorectal cancer. Patients will be studied with 124I-huA33 positron-emission tomography (PET), and in the subset of patients scheduled for surgery, based on clinical indications, ex vivo quantitation of tumor uptake will also be performed. Patients will receive a single intravenous or intraarterial infusion of 4 mCi-10mCi /10mg 124I-huA33 in 5-30ml of 5% human serum albumin (HSA), over 5-10 minutes. Patient will either receive the 124I-huA33 intravenously (IV) or intraarterially (IA) to determine if there is an advantage of the IV vs the IA route. Following injection with 124I-huA33, on study days 2, 3, and/ or 4, patients will have the option to receive up to 2g/1kg of Immune Globulin (IVIG).

Blood samples will be obtained for pharmacokinetic analysis at 5, 15, 60, and 120 minutes after completion of IV or IA infusion, on day 2, 3, and/ or 4, and before and after the PET scan on the day of surgery or last imaging day (day 8 + 3). Patients scheduled for surgery will undergo a PET scan of the abdomen and pelvis 1-6 hours prior to surgery.

In those patients undergoing surgery, surgery (or biopsy) will be scheduled to occur day 8 (± 3 days) days after administration of 124I-huA33. Biopsy sites may include tumor, tumor bed, regional nodes, portal, suprapancreatic, celiac nodes and the retroperitoneum. Tumor and normal tissue obtained at surgery (or biopsy), and serum will be measured for estimation of percent-injected dose per gram of tumor, normal liver, and serum. Tissue samples will be obtained for autoradiography and immunohistochemistry as an additional assessment of tumor targeting.

Blood samples to determine immunogenicity will be taken at baseline and at 4 weeks.

Toxicity assessments will be made throughout the study period.

Inclusion Criteria:

• primary metastatic colorectal carcinoma
• candidate for clinically indicated surgery/biopsy
• expected survival of at least 3 months
• Karnofsky performance status >70 (ECOG0 or 1)
• Age 18 or older
• women of childbearing potential with confirmed negative pregnancy test
• Laboratory results within 2 weeks of study day 1 that show acceptable hematological levels.

Exclusion Criteria:

• clinically significant cardiac disease
• Active CNS tumor involvement
• Previous treatment with A33 or its fragment and/or positive test for huA33 human anti-human antibodies
• women who are pregnant or breast-feeding
• participation in any other clinical trial involving another investigational agent within 4 weeks prior to enrollment