Immunohistochemical staining of the tumor. A, The cells were entirely positive for CK. B, The tumor cells were focally positive for Vimentin. C, Focal positive expression of CEA was present in the tumor cells. D, The area showed the transition from adenomatous hyperplasia (black arrow) to adenocarcinoma (red arrow). Ki67 index was less than 5% in adenomatous hyperplasia; in contrast, Ki67 index was approximately 40% in adenocarcinoma.