TNM staging of colorectal carcinoma: issues and caveats.

The TNM staging system of the American Joint Committee on Cancer and the Union for International Cancer Control provides the most reliable guidelines for the prognostication and treatment of colorectal carcinoma. However, issues and caveats exist in the application of this system, mostly relating to the definition of the staging parameters and the pathologic interpretation of the gross and microscopic findings of the resected specimens. This article highlights some of the major issues in both areas. First, it assesses the definition of selected staging parameters, including pTis, pT4a versus pT4b, tumor deposits/N1c, ypT/ypN, and the TNM for rectal versus anal carcinoma. Second, it discusses major problematic areas in the pathologic interpretation of "pseudoinvasion" versus true invasion, deep pT2 versus superficial pT3, serosal involvement, radial margin, total mesorectal excision specimens, and postneoadjuvant chemoradiation rectal resections. The article also provides a brief discussion about some of the major adjunct histopathologic prognostic factors, such as medullary-type histology and tumor differentiation.