Patients will receive an intravenous (IV) infusion of 188Re-PTI-6D2. Patients will undergo serial gamma scans at specified time points. Blood samples will be obtained prior to dosing and at specified intervals for PK measurements of the mAb as well as for measurement of serum radioactivity. Urine will be collected to measure excreted radioactivity. Patients will be closely monitored for safety throughout the duration of the study. Patients will remain at the study center for 48-72 hours after infusion of the radiolabeled dose to allow adequate time for post-treatment safety observation and rhenium decay. No investigational or commercial agents or therapies other than the study agent may be administered with the intent to treat the patient's malignancy during the inpatient treatment period.