Anal cancer

The anus is the name for the muscular area at the very end of the large bowel. It is the muscle which opens and closes to control bowel movements, and is where the bowel opens to the outside of the body. This muscle is also called a sphincter.

The most common type of anal cancer is squamous cell. Other rarer types are basal cell, adenocarcinoma and melanoma. This information deals with the treatment of squamous cell carcinoma.

Diagram showing the position of the anus

Causes of anal cancer

Cancer of the anus is rare. Less than 400 people are diagnosed with this type of cancer each year in the UK. It is slightly more common in women than in men. As with most cancers the cause of anal cancer is unknown.

Signs and symptoms

The most common symptoms of anal cancer are bleeding from the rectum and pain. Some people develop small firm lumps which may be confused with piles (haemorrhoids). Other symptoms include discomfort, itching and a discharge of mucous (a jelly-like substance) from the anus. Faecal incontinence (a reduced ability to control bowel function) may also occur. Anal cancer can appear as an ulcerated area and may spread to the skin of the buttocks.

It is known that anal cancer is more common in gay men. It is also more likely to develop in people who have had a particular virus infection called the human papilloma virus (HPV). The risk of having HPV increases with the number of sexual partners you have. Anal cancer is also more common in people who have a lowered immunity due to medical conditions, such as HIV. Cigarette smoking may also increase a person’s risk of developing anal cancer.

How it is diagnosed

Usually you begin by seeing your GP who will examine you and refer you to a specialist in bowel conditions (gastroenterologist). The doctor at the hospital will take your full medical history, do a physical examination and take blood samples to check your general health. Before the doctor can make a firm diagnosis of anal cancer a number of tests will have to be done.

Rectal examination This is also sometimes known as a PR examination and is where the doctor examines your back passage with a gloved finger.

Biopsy A small sample of cells is taken from the tumour so that it can be examined under a microscope. Usually this involves using either a special biopsy device (known as a punch biopsy) or the doctor can cut a small piece away from the tumour (known as an incisional biopsy). This can be done under local or general anaesthetic.

X-rays These may be taken to show if there has been any spread of the cancer.

Ultrasound scan This is a simple scan that uses sound waves to form a picture of the inside of the abdomen. These scans are done in the hospital's scanning department. Once you are lying comfortably on your back, a gel is spread onto your abdomen. A small device is then rubbed over the area. The sound waves are converted into a picture using a computer. The test is completely painless and takes 15–20 minutes.

You may also have an ultrasound scan known as an endoanal ultrasound. For this scan a small probe is passed into the rectum, which can show the size and extent of the tumour.

CT (computerised tomography) scan This is a more sophisticated type of x-ray which builds up a three-dimensional picture of the inside of the body. The scan is painless but takes longer than an x-ray (10–30 minutes). It may be used to identify the exact site of the tumour or to check for any spread of the cancer. Most people who have a CT scan are given a drink or injection to allow particular areas to be seen more clearly. Before having the injection or drink, it is important to tell the person doing this test if you are allergic to iodine or have asthma.

MRI (magnetic resonance imaging) scan This test is similar to a CT scan, but uses magnetic fields instead of x-rays to form a series of cross-sectional pictures of inside the body. During the scan you will be asked to lie very still on the couch inside a metal cylinder. You will usually be given an injection to allow the pictures to be seen more clearly.

The test can take about 30 minutes and is completely painless, although the machine is quite noisy. If you don’t like enclosed spaces you may find the machine claustrophobic. You will be given earplugs or headphones and you can usually take someone with you into the room to keep you company. A two-way intercom enables you to talk with the people controlling the scanner.

Staging

The 'stage' of a cancer is a term used to describe its size and whether it has spread beyond its original site. Knowing the particular type and the stage of the cancer helps the doctors to decide on the most appropriate treatment.

Cancer can spread in the body, either in the bloodstream or through the lymphatic system. The lymphatic system is part of the body’s defence against infection and disease. The system is made up of a network of lymph glands (also known as lymph nodes) that are linked by fine ducts containing lymph fluid.
Your doctors will usually check the nearby lymph nodes when staging your cancer.

• 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 nearby lymph nodes or to other parts of the body.
• Stage 3A The cancer has spread to the lymph nodes close to the rectum, or to nearby organs such as the bladder or vagina.
• Stage 3B The cancer has either spread to the lymph nodes in the groin and pelvis, or to the lymph nodes close to the anus as well as nearby organs, such as the bladder or vagina.
• Stage 4 The cancer has spread to lymph nodes in the abdomen or to other parts of the body, such as the liver.

A different staging system called the TNM staging system is sometimes used instead of the number system described.

• T describes the size of the tumour and whether it has spread into nearby 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 (secondary or metastatic cancer).

Although this system is more complex, it can give more precise information about the tumour stage.

If the cancer comes back after initial treatment, this is known as recurrent cancer.

Grading

Grading refers to the appearance of the cancer cells under the microscope and gives an idea of how quickly the cancer may develop. Low-grade means that the cancer cells look very like normal cells. They are usually slow-growing and are less likely to spread. In high-grade tumours the cells look very abnormal, are likely to grow more quickly and are more likely to spread.