A 64-year-old woman was diagnosed with unresectable pancreatic cancer and underwent chemotherapy. However, the number of leukocytes significantly increased as the disease progressed. Serum G-CSF values also increased, and she eventually died on day 511 after diagnosis. Immediately after autopsy, immunohistochemical staining with an anti-G-CSF monoclonal antibody was positive in the poorly differentiated adenocarcinoma area of the primary pancreatic cancer and liver metastatic foci, but negative in the well-differentiated tubular adenocarcinoma part of the primary pancreatic cancer. During de-differentiation, invasive pancreatic ductal carcinoma appeared to have changed to a tumor that produced G-CSF.