On the use and abuse of X in the TNM classification.

The tumor, lymph node, metastasis (TNM) classification system that has been in use worldwide since the 1980s was built on the premise that the anatomic extent of a majority of solid tumors is one of the most robust prognostic markers in cancer management. The TNM system is used by physicians and cancer registrars to categorize patients into important groups for treatment planning, clinical trials, and follow-up management. Although the TNM system has been evolving since the late 1940s, important additions to the staging taxonomy have mandated the development of important revisionary milestones, which add new clinical, pathologic, and molecular markers to the foundation of the system represented by the tumor, lymph node, and metastatic categories. The latest, sixth edition of the International Union Against Cancer (UICC) and American Joint Committee on Cancer (AJCC) continues this tradition and attempts to define parameters to reduce the subjectivity of cancer staging. Through discussions with physicians and registrars and through review of inquiries to the UICC and AJCC seeking clarification of staging guidelines, there remain areas of elusiveness and uncertainty in assigning proper staging categories. One of the most frequent of these conundrums is in the use of the “X” suffix, especially when assigned to the N or M categories. The proper use of X is to denote the absence or uncertainty of assigning a given category (T, N, or M) when all reasonable clinical or pathologic maneuvers have been used in staging. To aid the clinician in the approach to lymph node staging, the pertinent literature has offered guidelines indicating the optimal number of lymph nodes that should be assessed pathologically to adequately stage a given solid tumor. It has become clear that improvements in staging and prognosis may depend heavily on the removal of a maximum number of lymph nodes whether these are positive or negative for tumor cells. 647