[A case of unknown primary cancer responding to TS-1].

A 65-year-old male showed elevated tumor marker and intra-abdominal lymph node (LN) swelling. PET revealed an accumulation of FDG at para-aortic LNs from the mediastinum to the inguinal region. Although many different examinations were performed to detect primary cancer, none was found. We diagnosed unknown primary cancer (UPC), and administered TS-1 (100 mg/day). Six months later, the tumor marker lowered and the LN swelling reduced. PET showed a little accumulation of FDG at intra-abdominal LN. An intra-abdominal LN biopsy was performed, and an adenocarcinoma was seen at a lymph vessel. Then, 15 months later, brain metastasis was recognized and 18 months later the patient died of systematic metastasis. Autopsy was not performed, and primary cancer was not seen till the end. TS-1 proved effective for the UPC.