Safety and Efficacy Study of Different Doses of 90Y-hPAM4 Combined With Gemcitabine in Pancreatic Cancer

Inclusion Criteria: * Male or female patients, \>18 years of age, who are able to understand and give written informed consent. * Histologically or cytologically confirmed pancreatic adenocarcinoma. * Stage III (locally advanced, unresectable) or Stage IV (metastatic) disease, including patients who underwent surgery but had incomplete resections. * Treatment naïve (no prior chemotherapy, radiotherapy or investigational agents for pancreatic cancer) * Karnofsky performance status \> 70 % (Appendix A). * Expected survival \> 3 months. * At least 4 weeks beyond major surgery and recovered from all acute toxicities * At least 2 weeks beyond corticosteroids, except low doses (i.e., 20 mg/day of prednisone or equivalent) to treat nausea or other illness such as rheumatoid arthritis * Adequate hematology without ongoing transfusional support (hemoglobin \> 11 g/dL, ANC \> 2,000 per mm3, platelets \> 150,000 per mm3) * Adequate renal and hepatic function (creatinine and bilirubin ≤ 1.5 X IULN, AST and ALT ≤ 2.0 X IULN) * Otherwise, all toxicity at study entry \<Grade 1 by NCI CTC v3.0. Exclusion Criteria: * Women who are pregnant or lactating. * Women of childbearing potential and fertile men unwilling to use effective contraception during study until conclusion of 12-week post-treatment evaluation period. * Known metastatic disease to the central nervous system. * Presence of bulky disease (defined as any single mass \>10 cm in its greatest dimension) * Patients with \>Grade 2 anorexia, nausea or vomiting, and/or signs of intestinal obstruction. * Prior radiation dose \>3,000 cGy to the liver, \>2,000 cGy to lungs and kidneys or prior external beam irradiation to a field that includes more than 30% of the red marrow. * Patients with non-melanoma skin cancer or carcinoma in situ of the cervix are not excluded, but patients with other prior malignancies must have had at least a 5-year disease free interval. * Patients known to be HIV positive, hepatitis B positive, or hepatitis C positive. * Known history of active coronary artery disease, unstable angina, myocardial infarction, or congestive heart failure present within 6 months or cardiac arrhythmia requiring anti-arrhythmia therapy. * Known history of active COPD, or other moderate-to-severe respiratory illness present within 6 months. * Known autoimmune disease or presence of autoimmune phenomena (except rheumatoid arthritis requiring only low dose maintenance corticosteroids). * Infection requiring intravenous antibiotic use within 1 week. * Other concurrent medical or psychiatric conditions that, in the Investigator's opinion, may be likely to confound study interpretation or prevent completion of study procedures and follow-up examinations.