Pathologies of Precursor Lesions of Biliary Tract Carcinoma

SIMPLE SUMMARY: Carcinomas and precursor lesions of the biliary tract belong to a spectrum of pancreatobiliary neoplasms that share common histology and cell lineages. High-grade biliary intraepithelial neoplasm (high-grade BilIN), intraductal papillary neoplasm of bile duct (IPNB), and intracholecystic papillary neoplasm of the gallbladder (ICPN) are the main biliary tract precursors. High-grade BilINs are microscopically identifiable intraepithelial neoplastic lesions, whereas IPNB and ICPN are grossly visible intraductal or intraluminal preinvasive neoplasms in the bile duct and gallbladder, respectively. These neoplasms show characteristic histologic features according to the four subtypes based on cell lineages and two-tiered grading, and they are not infrequently associated with foci of stromal invasion at the time of surgical resection. In addition, these precursors, particularly high-grade BilINs, are frequently identified in the biliary mucosa surrounding biliary tract carcinomas (BTCs). Taken together, the progression of these precursors to invasive carcinoma may be a major process in biliary carcinogenesis. ABSTRACT: Carcinomas and precursor lesions of the biliary tract belong to a spectrum of pancreatobiliary neoplasms that share common histology and cell lineages. Over the past two decades, preinvasive precursors to biliary tract carcinomas (BTCs) have been identified such as high-grade biliary intraepithelial neoplasm (high-grade BilIN), intraductal papillary neoplasm of bile duct (IPNB) and intracholecystic papillary neoplasm of the gallbladder (ICPN). While a majority of these precursors may arise from the biliary tract mucosa, some originate from the peribiliary glands and Rokitansky-Aschoff sinuses in the walls of the biliary tract. High-grade BilIN is a microscopically identifiable intraepithelial neoplasm of the biliary tract, whereas IPNB and ICPN are grossly visible intraductal or intraluminal preinvasive neoplasms in the bile duct and gallbladder, respectively. These neoplasms show characteristic histologic features according to four cell lineages and two-tiered grading, and show intraepithelial spreading to the surrounding mucosa and involve non-neoplastic glands in the walls of the biliary tract. These precursors are not infrequently associated with stromal invasion, and high-grade BilIN, in particular, are frequently identified in the surrounding mucosa of BTCs. Taken together, it seems likely that progression from these precursors to invasive carcinoma is a major process in biliary carcinogenesis.