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Author: Dr. Francesc Tresserra i Casas

What does the staging of a tumour mean?

The staging of a tumour is a internationally recognised method to classify into categories the characteristics of a tumour. This system has been designed by the International Union Against Cancer and is known with the acronym TNM. In this acronym, the T stands for the size or extension of the tumour in the organ where it is located, the N represents the involvement of regional lymph nodes and the M represents the presence of distant metastasis.

By means of this system, it is possible to identify the mean characteristics that will define the tumour prognosis, which will be correctly interpreted by any physician in charge of the patient.

What is the staging of colorectal cancer?

T category (primary tumour)

Tx: No primary tumour found.

TO: No evidence of primary tumour.

Tis: Carcinoma in situ: Intraepithelial lesion or invading its own sheet.

T1: The tumour invades the submucosa.

T2: The tumour invades its own mucosa.

T3: The tumour extends beyond its own muscular layer and invades the subserosa or pericolonic or perirectal tissue void of peritoneum.

T4: The tumour invades directly the organs or structures and/or perforates the visceral peritoneum.

*The Tis stage includes the presence of tumoral cells in the glandular basal membrane (intraepithelial) or in its own sheet (intramucosal), without extension through the muscularis mucosa.

** The direct invasion in T4 includes the invasion of other colorectal segments through the serosa. Any tumour that adheres macroscopically to other organs or structures is classified as T4; however, if microscopically there is no evidence of tumoral cells in the adhesion, it is classified as pT3.

N category (regional lymph nodes)

Nx: Regional lymph nodes were not assessed.

NO: There is no metastasis in the regional lymph nodes.

N1: Metastasis in 1 to 3 regional lymph nodes.

N2: Metastasis in 4 or more regional lymph nodes.

M category (Distant metastasis)

Mx: Distant metastasis was not assessed.

MO: There is no distant metastasis.

M1: Presence of distant metastasis.

Reference: Sobin LH, Wittekind Ch. TNM classification of malignant tumors. Wiley-Liss: New York, 2002:72-76.