The stage of a cancer describes its size and whether it has spread beyond its original area of the body. Knowing the extent of the cancer helps the doctors to decide on the most appropriate treatment. Often, the exact stage of a bowel cancer can only be known after it has been removed by surgery.
Generally, cancer of the large bowel is divided into four stages:
small and localised (stage A)
spread into surrounding structures (stages B and C)
or spread to other parts of the body (stage D).
If the cancer has spread to distant parts of the body, this is known as secondary cancer (or metastatic cancer).
Doctors often use a staging system created by a pathologist called Dukes to describe large bowel cancer.
The Dukes staging system
Dukes A: The cancer is contained within the bowel wall.
Dukes B: The cancer has spread through the muscle of the bowel wall, but the lymph nodes are not affected.
Dukes C: The cancer has spread to one or more of the lymph nodes close to the bowel. Lymph nodes are usually the first place the cancer spreads to.
Dukes D: The cancer has spread to another part of the body such as the liver or the lungs (secondary cancer).
TNM staging system
The Dukes system is gradually being replaced by the TNM staging system.
T describes the size of the tumour and if it has spread into the bowel wall.
N describes whether the cancer has spread to the lymph nodes.
M describes whether the cancer has spread to another part of the body, such as the liver or the lungs (secondary or metastatic cancer).
Although this system is more complex, it can give more precise information about the tumour stage than the Dukes method.
If the cancer comes back after initial treatment it is known as recurrent cancer.
Grading refers to the appearance of the cancer cells under the microscope. The grade gives an idea how quickly they may develop.
There are three grades:
grade 1 (low-grade),
grade 2 (moderate or intermediate grade)
grade 3 (high-grade).
Low-grade means that the cancer cells look very like the normal cells of the bowel. They are usually slow-growing and are less likely to spread.
In high-grade tumours the cells look very abnormal. They are likely to grow more quickly and are more likely to spread.