Beating bowel cancer together

Diagnosis and staging of anal cancer

How is it diagnosed?

Your GP will take a history of your health and current symptoms. They are likely to do a physical examination of the abdomen, and a detailed examination (using a gloved finger) of the anus and rectum (back passage). They may also request a blood test to check for anaemia and any underlying health problems. If your GP suspects that you may have cancer, they will refer you urgently to a hospital colorectal specialist for diagnosis.

Special tests at the hospital may include:

  • Proctoscopy or sigmoidoscopy - a thin tube for looking into the rectum
  • Colonoscopy – a thin tube to look at the lining of your whole bowel
  • Ultrasound scan using a probe inserted into the rectum
  • Biopsy of any abnormal lumps or tissue for microscopic examination (usually under general anaesthetic as this is more comfortable)

If the test results show any suspicious findings you will then be referred for a CT scan of chest, abdomen and pelvis and a pelvic MRI (magnetic resonance imaging) scan to help your specialist plan the treatment that is best for you.

Staging and grading of anal cancer

Anal cancer tumours usually remain within the anal canal. However, cancer cells can spread beyond the tissue of the anus. Anal cancer can also spread locally and invade other pelvic organs such as the vagina, prostate gland or bladder. Knowing what stage a cancer is at will help the doctors decide on the most appropriate treatment pathway for you.

The most common staging system is the TNM system.

TNM system

  • T (tumour) – describes the size and location of the tumour
  • N (nodes) -  describes whether the cancer has spread to the lymph nodes
  • M (metastases) – describes whether the cancer has spread (metastasised to other parts of the body)



Doctors assign the stage of the cancer by combining the T, N, M.

Stage 0: also known as anal carcinoma in situ (AIN) or Bowen’s disease.

Stage 1: the cancer only affects the anus and is smaller than 2cm in size. It has not begun to spread into the sphincter muscle.

Stage 2: the cancer is bigger than 2cm in size, but has not spread into the lymph nodes or other parts of the body.

Stage 3: the cancer is larger than 5cm and has spread into the lymph nodes, or to nearby organs such as the vagina or bladder.

Stage 4: the cancer has spread to other more distant parts of the body, e.g. the liver.


Updated August 2018

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