Cancer of unknown primary site in which tumor marker-oriented chemotherapy was effective and pancreatic cancer was finally confirmed at autopsy.

We report a 47-year-old man with cancer of unknown primary site in whom pancreatic cancer was confirmed at autopsy. Although a primary lesion was not confirmed, we planned to perform tumor marker-oriented chemotherapy because pancreatic cancer was suspected as the primary lesion based on tumor markers and pathological findings from metastatic lymph node. Neither S-1 nor gemcitabine was effective. However, gemcitabine combined with low-dose cisplatin therapy resulted in a marked decrease in the size of tumors. Microscopic examination at autopsy revealed poorly differentiated adenocarcinoma in the pancreatic head, although a pancreatic mass was not clear macroscopically.