When a rare type of melanoma affects the anus and/or rectum it’s known as anorectal melanoma. This information describes anorectal melanoma, its symptoms, diagnosis and possible treatments.
You may also find it helpful to read our general information about malignant melanoma.
Anorectal melanoma is melanoma affecting the anus and/or rectum. Melanoma is a cancer that develops from cells called melanocytes. Melanocytes produce the pigment melanin, which is responsible for the colour of our skin. These cells are found in many places in our body, including the skin, hair and lining of the internal organs such as the anus and rectum.
The anorectal area is the third most common site for melanoma, after the skin and eye. However, it’s still a rare form of cancer; making up less than one in a hundred (1%) of all melanomas and between 1-2 in a hundred (1-2%) of all anorectal cancers. Anorectal melanoma can occur in several places. These include the rectum, anal canal (the junction between the anus and rectum) and the anus. Most people with anorectal melanoma are aged 60-80 and it’s also more common in women.
Causes of anorectal melanoma
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This is a rare type of tumour and, as for many other forms of cancer, the exact cause is unknown. We know that exposure to ultraviolet (UV) rays (either from the sun or sunbeds) increases the risk of developing melanoma of the skin.
However, there doesn't appear to be a link between UV ray exposure and the development of anorectal melanoma.
Signs and symptoms of anorectal melanoma
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A number of these cancers lack the normal dark colouring associated with melanomas and are known as amelanotic. This can make them more difficult to diagnose. People are often treated initially for piles (haemorrhoids). Symptoms include pain, rectal bleeding, a change in bowel habit (diarrhoea or constipation), piles, mucous discharge, tiredness and weight loss. All of these symptoms can also be caused by many other bowel conditions.
How anorectal melanoma is diagnosed
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Usually, you begin by seeing your GP (family doctor) who will do an examination of your back passage.
If your GP thinks that your symptoms could be caused by cancer, or if they aren't sure what the problem is, they will refer you to a hospital specialist. At the hospital, the doctor will ask you about your medical history before doing a physical examination. This will include a rectal examination. To do this, the doctor places a gloved finger into your back passage to feel for any lumps or swellings. This examination may be slightly uncomfortable but it is not painful. The doctor will also check whether or not the lymph nodes in the groin are enlarged. You may then have some of the following tests:
A small sample of tissue may be taken from the suspicious area and examined under a microscope. This can be done using a local anaesthetic so that the area is numb.
CT (computerised tomography) scan
A CT scan takes a series of x-rays that build up a three-dimensional picture of the inside of the body. The scan is painless and takes 10–30 minutes. It may be used to see if the cancer has spread to other areas of the body such as the liver, lungs or brain. CT scans use a small amount of radiation, which is very unlikely to harm you and won't harm anyone you come into contact with. You will be asked not to eat or drink for at least four hours before the scan.
You may be given a drink or injection of a dye, which allows particular areas to be seen more clearly. This may make you feel hot all over for a few minutes. If you’re allergic to iodine or have asthma, you could have a more serious reaction to the injection, so it's important to let your doctor know beforehand.
MRI (magnetic resonance imaging) scan
This test is similar to a CT scan but uses magnetism instead of x-rays to build up a detailed picture of areas of your body. Before the scan you may be asked to complete and sign a checklist. This is to make sure that it’s safe for you to have an MRI scan.
Before having the scan, you’ll be asked to remove any metal belongings, including jewellery. Some people are given an injection of dye into a vein in the arm. This is called a contrast medium and can help the images from the scan show up more clearly. During the test, you will be asked to lie very still on a couch inside a long cylinder (tube) for about 30 minutes. It is painless but can be slightly uncomfortable, and some people feel a bit claustrophobic during the scan. It’s also noisy, but you’ll be given earplugs or headphones.
Samples of your blood may be taken to check your general health, the number of cells in your blood (blood count) and to see how well your kidneys and liver are working.
The stage of a cancer is a term used to describe its size and whether or not 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 for you.
The most commonly used staging system is called the TNM system:
T refers to the size of the primary tumour (where the cancer first starts in the body).
N refers to which lymph nodes are affected, if any.
M refers to metastatic disease (when the cancer has spread to other parts of the body).
The T, N and M will often have numbers attached to describe the detail. For example, a T1 tumour may be very small and just in one layer of tissue, whereas a T4 tumour may be a larger size and spread through several layers of tissue.
The exact details of the T, N and M will depend on the type of cancer.
In addition to TNM staging, you’ll probably hear the doctors use a number staging system. There are usually three or four number stages for each cancer type.
Stage 1 describes a cancer at an early stage when it is usually small in size and hasn’t spread, whereas stage 4 describes cancer at a more advanced stage when it has usually spread to other parts of the body. Stages 2 and 3 are in-between these stages.
The number stages are made up of different combinations of the TNM stages.
So a stage 1 cancer may be described as either: T1, N0, M0 or T2, N0, M0.
Number stages may also be subdivided to give more detailed information about tumour size and spread. For example, a stage 3 cancer may be subdivided into stage 3a, stage 3b and stage 3c. A stage 3b cancer may differ from a stage 3a cancer in either the tumour size or if the cancer has spread to lymph nodes.
Talking about staging
In the last few years, staging systems have become increasingly complex and they now describe the size and spread of different types of cancer in much greater detail. This can be very helpful in planning the details of treatment or predicting outcomes.
However, doctors will often use a much simpler approach when talking about staging. They might use words like ‘early’ or ‘local’ if the cancer hasn't spread, ‘locally advanced’ if it has begun to spread into surrounding tissues or nearby lymph nodes, or ‘advanced’ or ‘widespread’ if it has spread to other parts of the body. Your doctors can give you more information about the stage of your particular cancer.
Treatment of anorectal melanoma
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Treatment for anorectal melanoma may be given at a specialist melanoma unit. A number of different treatments are used for anorectal melanoma, depending on the size and position of the tumour, and other factors such as your general health and fitness.
The aim of the treatment is usually to remove all or as much of the cancer as possible. It can also be given to try to destroy any remaining cancer cells and reduce the chance of the cancer returning. Treatment may also be given to relieve symptoms when the cancer has spread to other parts of the body.
There are two main types of surgery that are carried out: local resection and abdominoperineal resection.
Wide local excision
This may be used for small tumours on the outside of the anus. This operation removes the area containing the cancer cells and a small area (margin) of normal looking tissue all around the tumour.
This reduces the chance of cancer cells being left behind. The anal sphincter (the muscle in the wall of the anal canal) isn't usually affected, and so most people are still able to move their bowels normally. This avoids the need for a colostomy.
Abdominoperineal (AP) resection
This is the removal of the anus and rectum. Some of the pelvic and groin lymph nodes are also normally removed. This operation is usually done for:
tumours that involve the anal sphincter
tumours that circle the anus and/or rectum
tumours that return after local excision.
An AP resection means that you have to have a permanent colostomy. This involves diverting the open end of the bowel on to the surface of the abdomen (tummy area), to allow faeces to be passed out of the body into a colostomy bag. The opening on the abdominal wall is known as a stoma.
Although the idea of a colostomy is often frightening and distressing at first, most people find that they adapt over time. You will be able to get support and advice from the stoma nurse in your hospital. We have more information about living with a colostomy.
Occasionally, a sentinel lymph node biopsy may be offered at the same time as your surgery. This involves a tiny amount of radioactive liquid and/or blue dye being injected around the area of the melanoma during the surgery. The lymph nodes close to the melanoma are scanned to see which one has first taken up the radioactive liquid and/or blue dye. The surgeon removes only the first lymph node that the radioactive liquid and/or dye goes into (the sentinel node), so that it can be tested to see whether it contains melanoma cells.
If the sentinel node doesn't contain melanoma cells, it's very unlikely that the other lymph nodes in the area have been affected by the melanoma and no further treatment is usually needed.
This method of checking the lymph glands is still being researched in clinical trials to see how effective it is.
This type of treatment uses high-energy rays to destroy the cancer cells, while doing as little harm as possible to normal cells. In external radiotherapy, a beam of radiation is directed at the area of the tumour. The treatment is normally given as small doses (called fractions) over a few days or weeks.
Radiotherapy may be given after a local resection to reduce the risk of the cancer returning. This is known as adjuvant treatment. In this situation, the lymph nodes in the abdomen and groin can also be treated. Additionally, radiotherapy may be given if the cancer returns or as a palliative treatment to control local symptoms.
During the treatment period, you may have changes in your bowel function such as diarrhoea or passing wind. These side effects can sometimes be reduced by avoiding particular foods. Towards the end of the treatment period you may have blistering and soreness of the skin around the anal area, and possibly in the groin areas too. Extreme tiredness (fatigue) is also a common side effect of radiotherapy.
These side effects usually decrease gradually once the treatment finishes, but it may take some months for any skin changes to return to normal. A small number of people find that their bowel function is permanently altered. It's important to discuss this with your doctor as it's often possible to find ways of reducing any problems. Your doctor or a dietitian at the hospital can give you more advice.
Dr Vincent Khoo explains what to expect from radiotherapy.
Chemotherapy is the use of anti-cancer (cytotoxic) drugs to destroy cancer cells. It may be given after surgery as an adjuvant treatment. It may also be given if surgery isn't possible or if the cancer returns. The most common chemotherapy drug used is dacarbazine (also known as DTIC).
The chemotherapy drug is usually given by injection into a vein (intravenously). It can temporarily reduce the number of normal cells in your blood. When your blood count is low, you're more likely to get an infection and you may tire very easily. During chemotherapy, your blood will be tested regularly and, if necessary, you may be given antibiotics to treat any infection. Blood transfusions may be given if you become anaemic due to chemotherapy.
Other side effects may include feeling sick (nausea) and vomiting. Your doctor can prescribe effective anti-sickness medicines to help control this. Some chemotherapy drugs can also make your mouth sore and cause small mouth ulcers. Rinsing your mouth regularly is important and your nurse can show you how to do this properly. If you don't feel like eating meals, you can supplement your diet with nutritious drinks or soups. A wide variety of drinks are available and you can buy them at most chemists. You can ask your doctor to refer you to a dietitian for advice about your diet.
In order to grow and divide, cancer cell ‘communicate’ with each other using chemical signals. Targeted therapies are drugs that interfere with this process, and so affect the cancer’s ability to grow.
This type of treatment may be used for people with anorectal melanoma that has spread to other parts of the body. It’s currently only available as part of a trial in the UK. It only works for people with changes in certain genes (BRAF and c-KIT). Your doctors will be able to discuss this further with you.
After your treatment is completed, you will have regular check-ups and possibly scans or x-rays. You will probably continue to have these tests for several years. If you have any problems or notice any new symptoms between these times, let your doctor know as soon as possible.
During diagnosis and treatment for cancer you are likely to experience different emotions, from shock and disbelief to fear and anger. At times, these emotions can be overwhelming and hard to control. These feelings are natural and it's important to be able to express them.
Everyone has their own way of coping with difficult situations. Some people find it helpful to talk to family or friends, while others prefer to seek help from people outside their situation. Some people prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is available if you need it. You may wish to contact our cancer support specialists for more information and support.
Colostomy Association offers support and information to anyone who has had, or is due to have, a colostomy.
This information has been compiled using a number of reliable sources, including:
Belli F, et al. Melanoma of the anorectal region. The experience of the National Cancer Institute of Milano. EJSO. 2009. 35: 757–762.
Bullard K, et al. Surgical Therapy for Anorectal Cancer. Journal of the American College of Surgeons. 2003. 196: (2) 206–211.
Droesch J, et al. Wide local excision or abdominoperineal resection as the initial treatment for anorectal melanoma. The American Journal of Surgery. 2005. 189: (4) 446–449.
Kim K, et al. Biochemotherapy in Patients with Metastatic Anorectal Mucosal Melanoma. Cancer. 2004. 100: (7) 1478–1483.
Malik A, et al. What is the best surgical treatment for anorectal melanoma? International Journal of Colorectal Disease. 2004. 19: (2) 121–123.
With thanks to: Professor Patrick O'Dwyer, Professor of Gastrointestinal Surgery; and the people affected by cancer who reviewed this edition. Reviewing information is just one of the ways you could help when you join our Cancer Voices network.