Biopsy and assessing the extent of the cancer

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Biopsy - to confirm the diagnosis

A biopsy is when a small sample of tissue is removed from a part of the body. The sample is then examined under the microscope to look for abnormal cells.

If you have a colonoscopy or sigmoidoscopy, the doctor or nurse can take a biopsy of any abnormal tissue. This is done by passing a thin grabbing instrument down a side channel of the colonoscope or sigmoidoscope.

Assessing the extent and spread

If you are confirmed to have colorectal cancer, further tests may be done to assess if it has spread. For example, a CT scan, an MRI scan, an ultrasound scan, or other tests. (There are separate leaflets which describe each of these tests in more detail.) This assessment is called 'staging' of the cancer. The aim of staging is to find out:

How much the tumour in the colon or rectum has grown, and whether it has grown partially or fully through the wall of the colon or rectum.
Whether the cancer has spread to local lymph nodes.
Whether the cancer has spread to other areas of the body (metastasised).

By finding out the stage of the cancer it helps doctors to advise on the best treatment options. It also gives a reasonable indication of outlook (prognosis). For colorectal cancer, it may not be possible to give an accurate staging until after an operation to remove the tumour.

A common staging system for colorectal cancer is called the Duke's classification. This is:

Duke A: the cancer is just in the inner lining of the colon or rectum.
Duke B: the cancer has grown to the muscle layer in the wall of the colon or rectum.
Duke C: the cancer has spread to at least one lymph node near to the colon or rectum.
Duke D: the cancer has spread to other parts of the body ('metastases' or secondary tumours). The most common sites for colorectal cancer to spread to are the liver and lungs.

Other classification systems are sometimes used. For example, the TMN classification system is being increasingly used.