[MOL] Colon Cancer Staging [01848] Medicine On Line


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[MOL] Colon Cancer Staging



Staging

When a cancer is diagnosed, tests will usually be done to assess whether
the tumour
has spread. This is called 'staging' the tumour and affects the
treatment that will be
offered.

Staging systems exist for most types of cancer. Staging is a way of
describing how
far a cancer has spread. It is used to decide what treatment is most
appropriate for
a particular case. It also helps ensure that when results of different
treatments are
compared, that similar cases are used in the analysis to avoid bias. If
cases of
differing severity are compared then the comparison is unlikely to give
useful
information. See Understanding Clinical Trials for further information.

When a cancer spreads to a site away from the area where it started (the
primary
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

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
staging
systems in use.


The Tumour Node Metastasis (TNM) system

This is an international system which uses 3 different numbers to
describe the
tumour. The primary tumour (T) is described on a scale of 1-4, 1 being a
small
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
or 1.

A tumour will thus be described, for example, as T3N0M0 which would be a

moderately large tumour not affecting adjacent organs, with no lymph
node or
distant spread.


Number staging systems

These typically give a score of 1-4 to describe the extent of spread. An
example of
such a system is given for breast cancer. Various systems exist for
different cancers
and are widely used, particularly for gynaecological cancer and
lymphoma. TNM
stages can be grouped together to give a single number so the systems
are
interchangeable.

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
four groups:

     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
same region.

     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
groupings.

           STAGE
                                T N M GROUPINGS
                                                             DUKES
            Stage I
                              T1

                              T2
                                        N0

                                         N0
                                                   M0

                                                   M0
                                                             Dukesí A
           Stage II
                              T3

                              T4
                                         N0

                                         N0
                                                   M0

                                                   M0
                                                             Dukesí B
           Stage III
                             any T

                             any T
                                        N1

                                       N2 , N3
                                                   M0

                                                   M0
                                                             Dukesí C
           Stage IV
                             any T
                                        any N
                                                   M1
                                                             Dukesí D





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