Polypoid invasive carcinoma of bile duct: report of four cases.

Recently, "polypoid invasive carcinoma (PICA)" showing grossly visible polypoid, invasive carcinoma with no adenoma component was proposed as a neoplastic polyp of the gallbladder. Herein, we report four cases of PICA of the bile duct. PICA cases of bile duct showed single, sessile polypoid growth grossly, and polypoid components were composed of invasive carcinoma of papillary/tubular patterns with active desmoplasia, and invaded directly and continuously into the bile duct wall and periductal tissue. While PICA and other intraductal papillary neoplasm of bile duct (IPNB) shared several features, PICA showed an invasive carcinoma growing in the duct lumen and also invading into the bile duct wall, thus different from IPNB which is the intraluminal polypoid, preinvasive epithelial neoplasia with back-to-back epithelial units. Taken together, PICA and IPNB could be differentiated from each other.