Pathologic staging of pancreatic, ampullary, biliary, and gallbladder cancers: pitfalls and practical limitations of the current AJCC/UICC TNM staging system and opportunities for improvement

Tumors of the ampulla-pancreatobiliary tract are encountered increasingly; however, their staging can be highly challenging due to lack of familiarity. In this review article, the various issues encountered in staging of these tumors at the pathologic level are evaluated and possible solutions for daily practice as well as potential improvements for future staging protocols are discussed. While N-stage parameters have now been well established (the number of lymph nodes required in pancreatoduodenectomies is 12), the T-staging has several issues: for the pancreas, the discovery of small cancers arising in intraductal papillary mucinous neoplasms (IPMNs) and mucinous cystic neoplasms (MCNs) necessitates the creation of substages of T1 (as T1a, b, and c); lack of proper definition of "peripancreatic soft tissue" and "common bile duct involvement" (as to which part is meant) makes T3 highly subjective. Increasing resectability of main vessels (portal vein) brings the need to redefine a "T" for such cases. For the ampulla, due to factors like anatomic complexity of the region and the under-appreciation of three-dimensional spread of the tumors in this area (in particular, the frequent extension into periduodenal soft tissues and duodenal serosa, which are not addressed in the current system and which require specific grossing approaches to document), the current T-staging lacks reproducibility and clinical relevance, and therefore, major revisions are needed. Recently proposed refined definition and site-specific subclassification of ampullary tumors highlight the areas for improvement. For the extrahepatic bile ducts, the staging schemes that use the depth of invasion may be more practical to circumvent the inconsistencies in the histologic layering of the ducts; better definition of terms like "periductal spread" is needed. For the gallbladder, since many gallbladder cancers are "unapparent" (found in clinically and grossly unsuspected cholecystectomies), establishing proper grossing protocols and adequate sampling are crucial. Since the gallbladder does not have the distinct layering of the other gastrointestinal organs, the definitions of Tis/T1a/T1b lack practicality, and therefore, "early gallbladder carcinoma" category proposed in high-risk regions may have to be recognized instead. Involvement of the Rokitansky-Aschoff sinuses should be a part of the evaluation and management of these early gallbladder cancers; for advanced cancers, documentation of hepatic versus serosal involvement is necessary. In summary, T-staging of ampulla-pancreatobiliary tract tumors has many challenges. Proper grossing and appreciation of histo-anatomic subtleties of this region are crucial in addressing these issues and achieving more applicable and clinically relevant staging systems in the future.