Staging is the assessment of the degree of spread of a tumor. The staging can be clinical or pathological.

Clinical staging is used alone in the following circumstances:

Pathological staging of colorectal cancer was historically undertaken by a number of different systems. The two used in Europe were the TNM and the older Dukes classification. Originally the Dukes classification used three stages: A, B, and C [4]. The latter was subsequently modified into stages C1 and C2, with the addition of a fourth stage, stage D [5] (see Table 23.6). The UICC and AJCC recently introduced the TNM staging system, which uses four stages (stages I–IV). The anatomic extent of cancer is described by assessing three components:

TNM is superior to Dukes because of the greater information it yields, and it is now the preferred system. However, there is controversy because the system is frequently updated. There have been various versions of the TNM staging; thus the version used should be specified (e.g., version 5, version 6, version 7). The most recent seventh edition of the TNM has introduced classification systems for gastrointestinal stromal tumors and neuroendocrine tumors. Currently the United Kingdom and a number of other countries advise using TNM 5 for colorectal cancer, whereas most countries have adopted TNM 7 (Table 23.7) since its introduction in 2009.