Abstract
In patients with cancer of unknown primary (CUP), the efficiency of reexamination in the improvement of the prognosis has not been demonstrated yet. In the present case, ampullary adenocarcinoma, initially diagnosed as CUP, was revealed by endoscopic forceps biopsy for the ampullary lesion progressing over time. Reexamination of the primary site in patients with CUP could contribute to better treatment options and improvement in the prognosis.