Clinicopathological characteristics of pancreatic ductal adenocarcinoma with invasive micropapillary carcinoma component with emphasis on the usefulness of PKCζ immunostaining for detection of reverse polarity

Invasive micropapillary carcinoma (IMPC) is a rare distinct histopathological subtype, characterized by the presence of carcinoma cells displaying reverse polarity. Only limited clinicopathological information is available regarding pancreatic IMPC. The aim of the present study was to clarify the clinicopathological features of pancreatic IMPC and the usefulness of protein kinase C (PKC)ζ immunostaining for the detection of reverse polarity. We reviewed 242 consecutive surgically resected specimens of pancreatic ductal adenocarcinoma and selected samples with an IMPC component. Clinicopathological characteristics were compared between the IMPC and non-IMPC groups. Immunohistochemical staining for PKCζ was performed using an autostainer. In total, 14 cases had an IMPC component (5.8%). The extent of IMPC component ranged from 5 to 20%. There were no significant differences in tumor location, T category, lymph node metastatic status, preoperative carbohydrate antigen 19-9 level, resection status and overall survival between the IMPC and non-IMPC groups. Immunostaining for PKCζ clearly showed reverse polarity of the neoplastic cells of IMPC. Although previous reports have shown that the presence of an IMPC component (>20% of the tumor) indicated poor prognosis, the present study demonstrated that presence of IMPC <20% did not suggest a worse prognosis.