A 74-year-old woman had an undifferentiated carcinoma with osteoclast-like giant cells (UCWOGC) in the body of the pancreas with massive portal vein tumor thrombus (PVTT). Because the PVTT progressed so rapidly into the right portal branch, the patient first underwent distal pancreatectomy and tumor thrombectomy to prevent life-threatening portal venous obstruction. Although a recurrent PVTT had developed early postoperatively, systemic gemcitabine treatment was so effective that it induced complete remission 5 months after the initiation of chemotherapy. The patient continued to be in complete response for 12 months, and has survived for 19 months since surgery.