Development of post-surgical staging
Development of post-surgical staging[edit source]
The first well-documented and tested staging system was that of Dukes. This classification system was based entirely on the extent of direct tumour spread through the bowel wall and the presence or absence of lymph node metastases in the resected specimen. Although Dukes staging was originally conceived for rectal cancer, it is also applicable to colon cancer. Dukes stages A, B and C correlate well with patient survival, and are easy to recall and apply. For these reasons the system is widely adopted and remains an objective, unambiguous classification adaptable to multidisciplinary patient care. However, the Dukes system does not address the important issue of ‘residual tumour’ identified by the surgeon at the time of bowel resection, either local due to tumour transection or due to known distant metastases.
The Dukes (A, B, C) system was further modified by Turnbull, who added a stage ‘D’ for cases with known distant metastases and locally unresectable tumour. Thus, Turnbull introduced the concept of clinicopathological staging in which residual tumour, found by the surgeon at the time of bowel resection, could determine the assigned stage. Clinicopathological staging has now gained wide acceptance as the preferred method of staging.
The ACPS system was recommended for use in Australia following two workshops on staging held in Brisbane in 1981. The system was validated using prospectively collected data from the Concord Hospital Colorectal Cancer Project. The ACPS is essentially a simplified version of the system used at Concord Hospital since 1971. The ACPS and Concord systems are shown in Table 8.1.
Table 8.1. ACPS/Concord substaging definitions[edit source]
|ACPS||Concord substage||Maximum spread|
|B||B1||Beyond muscularis propria|
|B2||Free serosal surface involvement by direct spread|
|C||C1||Local nodes involved|
|C2||Apical nodes involved|
|D||D1||Tumour transected (histological)|
|D2||Distant metastases (clinical or histological)|
A TNM system acceptable to both the Union Internationale Contre Le Cancer (UICC) and the American Joint Committee for Cancer (AJCC) was agreed in 1986 with the aim of attempting to achieve uniformity in staging of Colorectal Cancer (Tables 8.2 and 8.3). The ‘p’ prefix is used to indicate postsurgical pathological staging. This system is now in its 8th edition (implementation date 1/1/2018) and has undergone several significant revisions to the numerical coding with successive editions, including interpretation of mesenteric lymph node and non-lymph node associated tumour deposits. Between the 6th and 7th editions of the AJCC cancer staging manual, the definitions of T4a and T4b were reversed, a code was added to indicate the presence of extramural tumour deposits in the absence of lymph node metastasis (N1c), and the MX code was deleted. In the 8th edition, the definitions of carcinoma in situ and lymph node status have been further refined. A separate M code has been introduced for peritoneal carcinomatosis, which has been separated out from M1b into M1c. The prognostic and predictive implications of microsatellite instability (MSI), mutations of KRAS, NRAS and BRAF are also discussed.
Table 8.2. Pathological TNM staging nomenclature[edit source]
|T — primary tumour|
|TX||Primary tumour cannot be assessed|
|T0||No evidence of primary tumour|
|Tis||Carcinoma in situ: intramucosal (involvement of lamina propria with no extension through muscularis mucosae)|
|T1||Tumour invades submucosa (through muscularis mucosae but not into the muscularis propria)|
|T2||Tumour invades muscularis propria|
|T3||Tumour invades through muscularis propria into pericolorectalic (subserosal) tissues|
|T4||Tumour invades the visceral peritoneum or invades or adheres to adjacent organ or structure|
|T4a||Tumour penetrates to the surface of the visceral peritoneum (including gross perforation of the bowel through areas of inflammation to the surface of the visceral peritoneum)|
|T4b||Tumour directly invades or adheres to other organs or structures|
|N - regional lymph node|
|NX||Regional lymph nodes cannot be assessed|
|NO||No regional lymph nodes metastases|
|N1||One to three regional nodes are positive (tumour in lymph nodes measuring >0.2mm), or any number of tumour deposits are present and all identifiable lymph nodes are negative|
|N1a||One regional lymph node is positive|
|N1b||Two or three regional lymph nodes are positive|
|N1c||No regional lymph nodes are positive, but there are tumour deposits in the
|N2||Four or more regional lymph nodes are positive|
|N2a||Four to six regional lymph nodes are positive|
|N2b||Seven or more regional lymph nodes are positive|
|M — distant metastasis|
|MO||No distant metastasis by imaging, etc; no evidence of tumour in distant sites or organs (This category is not assigned by pathologists.)|
|M1||Metastasis to one or more distant sites or organs or peritoneal metastasis is identified|
|M1a||Metastasis to one site or organ is identified without peritoneal metastasis|
|M1b||Metastases to two or more sites or organs is identified without peritoneal metastasis|
|M1c||Metastasis to the peritoneal surface is identified alone or with other site or organ metastases|
Table 8.3. AJCC prognostic stage groups[edit source]
|IVA||Any T||Any N||M1a|
|IVB||Any T||Any N||M1b|
|IVC||Any T||Any N||M1c|
Source: AJCC 2017
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