TNM staging system
T – describes how far the tumour has grown into the wall of the bowel, and whether it has grown into nearby tissues or organs.
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 lungs (secondary or metastatic cancer).
The bowel wall is made up of layers of different tissues.
- Tis means the cancer is at its earliest stage (in situ). It is growing into the mucosa but no further.
- T1 means the tumour is only in the inner layer of the bowel (submucosa).
- T2 means the tumour has grown into the muscle layer of the bowel wall but no further.
- T3 means the tumour has grown through the muscle layer of the bowel and into the tissues that surround the bowel, but not through the membrane covering the outside of the bowel (peritoneum).
- T4 means the tumour has grown through the outer layer of the bowel wall (serosa) and through the peritoneum. A tumour at this stage can be described as T4a or T4b:
- T4a means the tumour has caused a hole in the bowel wall (perforation) and cancer cells have spread outside the bowel.
- T4b means it has grown into other nearby structures, such as other parts of the bowel or other organs in the body.
Cross-section diagram showing the different layers of the bowel and the different T stages of cancer
N – Nodes
N0 means no lymph nodes contain cancer cells.
N1 means there are cancer cells in up to three nearby lymph nodes or there are cancer cells in the tissues around the bowel.
N2 means there are cancer cells in four or more nearby lymph nodes.
M – Metastases
M0 means the cancer has not spread to distant organs.
M1 means the cancer has spread to distant organs such as the liver or lungs.
Number staging system
Information from the TNM system can be used to give a number stage from 0 to 4.
Stage 0 – The cancer is at its earliest stage and is only in the mucosa (Tis N0 M0).
Stage 1 – The cancer has grown into the submucosa or muscle, but has not spread to the lymph nodes or elsewhere (T1 N0 M0 or T2 N0 M0).
Stage 2 – The cancer has grown through the muscle wall or through the outer layer of the bowel and may be growing into tissues nearby. The cancer has not spread to the lymph nodes or elsewhere (T3 N0 M0 or T4 N0 M0).
Stage 3 – The tumour is any size and has spread to lymph nodes nearby, but has not spread anywhere else in the body (Any T N1 M0 or Any T N2 M0).
Stage 4 – The tumour is any size. It may have spread to nearby lymph nodes. The cancer has spread to other parts of the body such as the liver or lungs (Any T Any N M1).
The grade describes how the cancer cells look and behave compared to normal cells. Doctors will look at a sample of the cancer cells under a microscope to find the grade of your cancer.
- Grade 1 (low-grade) – The cancer cells tend to grow slowly and look similar to normal cells (they are well differentiated). These cancers are less likely to spread than higher-grade cancers.
- Grade 2 (moderate-grade) – The cancer cells look more abnormal.
- Grade 3 (high-grade) – The cancer cells tend to grow more quickly and look very abnormal (they are poorly differentiated). These cancers are more likely to spread than low-grade cancers.
Doctors may do further tests on the bowel cancer cells from a biopsy taken when you were first diagnosed. Or they may test bowel cancer cells that were removed during surgery. Sometimes they may need to take a second sample of bowel cancer cells if the cancer has spread to another part of your body.
Not everyone will need all the following tests. Your doctor will explain which tests are needed in your situation.
Bowel cancer cells may be tested for micro-satellite instability (MSI). DNA carries all your genetic information inside the cell. When a cell divides normally, a repair system ensures that the new DNA is identical to the original DNA by repairing any changes to the DNA. With MSI, this repair system is faulty. This test can detect if this is the case .
MSI testing can help you and your doctor decide whether you may need further genetic tests. Genetic tests may tell you whether you have bowel cancer caused by an inherited condition called Lynch syndrome. People with Lynch syndrome have an increased risk of developing bowel cancer at a young age.
Checking the blood vessels and nerves
Cancer and surrounding tissues removed during surgery are checked to see if the cancer has spread into blood vessels or nerves within the tissues. If cancer has spread into the blood vessels or nerves, it can increase the risk of the cancer spreading to other parts of the body. Knowing more about this can help you and your doctor decide whether you may need further treatment after your surgery.
RAS gene mutation
Doctors may test the cancer cells for certain gene changes (mutation). In bowel cancer doctors check for a change called the RAS gene mutation. RAS genes help control cell growth. Changes to RAS genes can affect what type of treatment you might have. For example, some targeted therapies do not work on bowel cancer that has the RAS gene mutation.
BRAF gene mutation
Doctors may also test the bowel cancer cells for a change in the BRAF gene. The BRAF gene makes a protein that is involved in cell growth. A change to this gene means that the protein becomes overactive which can make cancer cells grow and divide more quickly.
Knowing whether you have the BRAF gene mutation can tell doctors more about how you might respond to certain treatments.
Below is a sample of the sources used in our bowel cancer information. If you would like more information about the sources we use, please contact us at email@example.com
R Glynne-Jones, PJ Nilson, C Aschele et al. ESMO-ESSO-ESTRO Clinical practice guidelines for diagnosis, treatment and follow up for anal cancer. July 2014. European Society of Medical Oncology. Available from www.esmo.org/Guidelines/Gastrointestinal-Cancers/Anal-Cancer (accessed October 2019).
National Institute for Health and Excellence (NICE). Colorectal cancer: diagnosis and management clinical guidelines. Updated December 2014. Available from www.nice.org.uk/guidance/cg131 (accessed October 2019).
Association of Coloproctology of Great Britain & Ireland (ACPGBI). Volume 19. Issue S1. Guidelines for the management of cancer of the colon, rectum and anus. 2017. Available from www.onlinelibrary.wiley.com/toc/14631318/19/S1 (accessed October 2019).
BMJ. Best practice colorectal cancer. Updated 2018. Available from www.bestpractice.bmj.com/topics/en-gb/258 (accessed October 2019).
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.
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