A Study of Fractionated 90Y-hPAM4 Plus Gemcitabine in Pancreatic Cancer Patients Receiving at Least 2 Prior Therapies.

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 IV (metastatic) disease, including patients who underwent surgery but had incomplete resections
* Previously treated and received two prior treatment regimens for advanced disease
* Karnofsky performance status ≥ 60 % (Appendix A)
* Expected survival ≥ 3 months
* At least 4 weeks beyond major surgery, 2 weeks beyond chemotherapy, radiotherapy, other experimental treatments
* 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 \> 9 g/dL, ANC \> 1,500 per mm3, platelets \> 100,000 per mm3)
* Adequate renal and hepatic function (creatinine and bilirubin ≤ 1.5 X IULN, AST and ALT ≤ 2.0 X IULN \[5.0 X IULN if due to liver metastases\])
* Otherwise, all toxicity at study entry ≤ Grade 1 by NCI CTC v3.0 or recovered to baseline or discussed with and agreed to with Immunomedics' Medical Monitor.

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 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 3-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 (other than stable atrial fibrillation) 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