The evolving TNM cancer staging system: an essential component of cancer care ============================================================================= * James Brierley Before therapy commences for any cancer patient, 3 essential factors should be known: the site of origin, the histological type (including grade) and the extent or stage of the cancer. Cancer staging is an important component, not only of patient care, but also of cancer research and control activities. The globally accepted method for describing the extent of cancer is the anatomically based TNM (tumour, node, metastases) staging system, which classifies the cancer as to its local, regional and distant extent. Developed in France in the 1940s by Pierre Denoix, the TNM classification has become the accepted basis of cancer staging. ![Figure1](http://www.cmaj.ca/https://www.cmaj.ca/content/cmaj/174/2/155/F1.medium.gif) [Figure1](http://www.cmaj.ca/content/174/2/155/F1) Box 1. The general rules of the TNM system change as new technologies in cancer diagnosis and treatment develop.1 For example, because sentinel nodes are now biopsied more frequently in several types of malignant diseases, including breast cancer and melanoma, the sn designation has been introduced to indicate that a pathologic categorization of a regional node was based on a sentinel-node biopsy rather than on a full nodal dissection (Box 1, Box 2). The prognostic significance of micrometastases and especially of isolated tumour cells, although still uncertain, can now be detected through improvements in immunohistochemistry, and should be reported. ![Figure2](http://www.cmaj.ca/https://www.cmaj.ca/content/cmaj/174/2/155/F2.medium.gif) [Figure2](http://www.cmaj.ca/content/174/2/155/F2) Box 2. In addition to new designations, the numbers of nodes to be examined in pathology specimens from various sites have been clarified. Note that when the number of lymph nodes resected is fewer than the number recommended for assessment (e.g., < 12 nodes in cases of colorectal cancer) and all nodes are judged to be negative for metastases, it is the N0 category that should be assigned. In such circumstances it is important *not* to record the cancer classification as NX, even though all of the nodes are negative. The inappropriate use of NX in situations such as this results in a loss of valuable information.2 With the increasing use of neoadjuvant therapy, which can affect the local and regional extent of a tumour, the prefix y is a useful tool. The insertion of y before the pathologic stage indicates that neoadjuvant therapy has been provided preoperatively, and that the pathologic extent of disease may therefore change. Changes in the definitions of TNM categories and the stage groupings of cancers at some of the major tumour sites are summarized in Table 1. The staging of tumours in less common sites such as hepatoma and melanoma has undergone major revision as well; details can be found in the International Union Against Cancer's *TNM Classification of Malignant Tumours* (sixth edition, Wiley-Liss; 2002), the American Joint Committee on Cancer's *AJCC Cancer Staging Manual* (likewise the sixth edition, Springer; 2002) and on the Web (at [www.cancerstaging.org/products/ajccproducts.html#guide](http://www.cancerstaging.org/products/ajccproducts.html#guide)). View this table: [Table1](http://www.cmaj.ca/content/174/2/155/T1) Table 1. An annual process is now in place for review of the literature to identify evidence supporting the need for changes to the TNM staging system. The evidence is then assessed by panels of site-specific experts with international recognition. Changes in the next (seventh) edition, due in 2009, will be evidence-based.3 The National Cancer Institute of Canada's Committee on Cancer Staging continues to act as a conduit for proposals for changes to the TNM classification. Any such proposals for change or comments about the changes in the sixth edition can be directed to the Committee on Cancer Staging, National Cancer Institute of Canada, 10 Alcorn Ave., Ste. 200, Toronto ON M4V 3B1. ## Footnotes * **Competing interests:** None declared. ## REFERENCES 1. 1. Sobin LH. TNM, sixth edition: new developments in general concepts and rules. Semin Surg Oncol 2003;21:19-22. [CrossRef](http://www.cmaj.ca/lookup/external-ref?access_num=10.1002/ssu.10017&link_type=DOI) [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=12923912&link_type=MED&atom=%2Fcmaj%2F174%2F2%2F155.atom) 2. 2. Greene FL, Brierley J, O'Sullivan B, Sobin LH, Wittekind C; International Union Against Cancer and American Joint Committee on Cancer. 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