When a cancer is diagnosed, tests will usually be done to assess whether
has spread. This is called 'staging' the tumour and affects the
treatment that will be
Staging systems exist for most types of cancer. Staging is a way of
far a cancer has spread. It is used to decide what treatment is most
a particular case. It also helps ensure that when results of different
compared, that similar cases are used in the analysis to avoid bias. If
differing severity are compared then the comparison is unlikely to give
information. See Understanding Clinical Trials for further information.
When a cancer spreads to a site away from the area where it started (the
site) this is called a 'secondary tumour' or 'metastasis'.
Cancer spreads in three main ways
By directly extending into adjacent structures
Through the blood stream
Through the lymphatic system
Staging systems typically will describe whether or not and to what
extent each of
these three sorts of spread has occured. There are two main sorts of
systems in use.
The Tumour Node Metastasis (TNM) system
This is an international system which uses 3 different numbers to
tumour. The primary tumour (T) is described on a scale of 1-4, 1 being a
tumour, 4 a large tumour affecting adjacent organs. Whether there is
spread to the
lymph nodes (N) is described on a scale of 0-3, 0 being no spread, 3
being a lot.
The presence of distant metastasis (M) is scored either 0 for no spread
A tumour will thus be described, for example, as T3N0M0 which would be a
moderately large tumour not affecting adjacent organs, with no lymph
Number staging systems
These typically give a score of 1-4 to describe the extent of spread. An
such a system is given for breast cancer. Various systems exist for
and are widely used, particularly for gynaecological cancer and
stages can be grouped together to give a single number so the systems
Classification of Colon and Rectal Cancer
Colon and rectal cancers are classified or staged at the time of surgery
and by microscopic
examination of the tumor cells removed during surgery. Cancers of the
colon and rectum use the
same staging systems.
There are two different methods of describing a colon or rectal cancer
stage, the modified Dukesí
classification and the TNM system of staging.
The modified Dukesí system of staging separates colorectal cancers into
Stage A - includes tumors that are found only in the inner wall of
the colon or rectum.
Stage B - includes tumors that have penetrated the muscle layer of
the bowel wall or
have gone through the bowel.
Stage C - includes tumors that have spread to lymph nodes in the
Stage D - includes tumors that have spread to distant sites, such
as the liver.
The TNM staging system is also used. This is the staging system
recommended by the American
Joint Commission on Cancer.
In this system three different characteristics of the tumor are coded.
"T" is used to describe the size and extent of the main tumor. The
T stage is numbered
1 through 4. Tis means the tumor is non-invasive (in situ). The
higher the number the
deeper the penetration through the bowel wall.
"N" is used to describe whether lymph nodes have any cancer cells
in them and the
number of nodes involved. N0 is used when no nodes are involved, N1
when 1- 3
nodes are involved and N2-3 when more than 3 are positive.
"M" is used to describe whether cancer has spread to other parts of
the body. M0
means that there is no evidence of distant metastatic disease.
Four stages (I-IV) may be described based on the T, N, and M
T N M GROUPINGS
N2 , N3
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