How is bowel cancer diagnosed?

Bowel cancer may be diagnosed after you visit your doctor with symptoms, or if a screening test shows signs that you might have bowel cancer.

You might have a number of tests to investigate your symptoms and confirm a diagnosis of bowel cancer, including: ^[15][16][17]

physical examination
tests to look for blood in your stools
blood test to check for anaemia (low haemoglobin which can make you feel tired and weak)., to check liver function (because bowel cancer can spread to the liver) or to check for tumour markers (substances that are produced by bowel cancer cells)
internal examination of the rectum, anus and colon – this may include a sigmoidoscopy or colonoscopy, in which a thin tube with a light and a camera on the end is passed through the rectum so that the doctor can look at the rectum and colon
imaging of the bowel, which may include a barium enema, computed tomography (CT) scan, ultrasound scan or magnetic resonance imaging (MRI) scan
a nuclear medicine scan, such as a positron emission tomography (PET) scan to look at the cancer. A weak radioactive substance is injected into the body to show the cancer in a clearer way, and see if it has spread to other parts of the body.
removal of a small piece of tissue from the bowel wall (biopsy) for examination under a microscope or laboratory testing.

Stages of bowel cancer

If you are diagnosed with bowel cancer, you might have more tests to determine the stage of the disease and whether the cancer has spread to other parts of the body. Knowing the stage of the disease helps your medical team plan the best treatment for you.

Bowel cancer is divided into 4 stages, depending on whether the cancer has spread through the bowel wall to other organs or lymph nodes: ^{[18][19][20][21]}

Stage 0 (carcinoma in situ) – there are abnormal cells in the bowel lining that may become cancerous; cancer has not spread beyond the bowel lining.
Stage I – the cancer has spread from the bowel lining to deeper layers of the bowel wall (submucosa or muscle); it has not spread to nearby lymph nodes or other parts of the body.
Stage II – the cancer has spread through the muscle of the bowel wall and may have spread to nearby organs; it has either not spread to nearby lymph nodes or has spread to 1–3 nearby lymph nodes, and has not spread to distant parts of the body.
Stage III – the cancer has spread to nearby lymph nodes and organs; it has not spread to distant parts of the body.
Stage IV – the cancer has spread through the lymph nodes or blood to other parts of the body such as the liver or lungs.

Tests to determine the stage of bowel cancer can include: ^[22]