What is anorectal 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 is still a rare form of cancer, making up less than one in a hundred (1%) of all melanomas and between one to two in a hundred (1–2%) of all anorectal cancers. Anorectal melanoma can occur in several places. These include: the rectum, anal canal (which is the junction between the anus and rectum) and the anus. Most people with anorectal melanoma are aged 60– 80. It is also more common in women.
Causes
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 does not appear to be a link between UV ray exposure and the development of anorectal melanoma.
Signs and symptoms
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 it is diagnosed
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 is not sure what the problem is, they will refer you to a hospital specialist. At the hospital, the doctor will take 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:
Biopsy 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. More commonly, excisional biopsies are done. This involves removing the whole tumour.
CT (computerised tomography) scan A CT scan takes a series of x-rays to build a three-dimensional picture of the inside of the body. The scan is painless but takes10–30 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.
MRI (magnetic resonance imaging) scan This type of scanner uses magnetism instead of x-rays to form a series of pictures of the inside of the body. The test can take about 30 minutes. It is completely painless, but some people feel a bit claustrophobic during the scan. It is also noisy and you will be given earplugs or headphones to wear.
Chest x-ray A chest x-ray is usually done to check whether or not the cancer has spread to the lungs.
Blood tests 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.
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 nodes (sometimes called lymph glands) that are linked by fine ducts containing lymph fluid.
A commonly used staging system for melanoma is described here:
- Stage 1A: The cancer is less than 0.75mm thick and is localised (has not spread to the lymph nodes
- Stage 1B: The cancer is between 0.76 and 1.5mm thick and is localised
- Stage 2A: The cancer is between 1.5 and 4.0mm thick and is localised
- Stage 2B: The cancer more than 4.0mm thick and is localised
- Stage 3: The cancer has spread to the lymph nodes in the groin and pelvis or to the lymph nodes close to the anus
- Stage 4: The cancer has spread to other parts of the body such as the liver, lungs or brain.
Treatment overview
A number of different treatments are used for anorectal melanoma, depending on the size and position of the tumour, as well as other factors such as your age and general health. 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.
Surgery
There are two main types of surgery that are carried out. These are local resection and abdominoperineal resection.
Local resection This may be used for small tumours on the outside of the anus. This operation removes only the area of the anus containing the cancer cells. The anal sphincter (the muscle in the wall of the anal canal) is not usually affected, and so most people are still able to move their bowels normally. This avoids the need for a colostomy.
Abdominoperitoneal (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:
- large tumours
- tumours which involve the anal sphincter
- tumours that are circling the anus and/or rectum
- tumours that return after local resection.
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. Cancerbackup nurses can provide you with more information about living with a colostomy
Occasionally sentinel lymph node biopsy may be offered at the same time as your surgery. This involves a tiny amount of radioactive liquid being injected around the area of the melanoma immediately after it is removed. The lymph nodes close to the melanoma are scanned to see which one has first taken up the radioactive liquid. A blue dye is also injected into the area of the melanoma during the operation. The dye stains the lymph nodes blue. The surgeon removes only the first lymph node that the fluid goes into (the sentinel node), so that it can be tested to see whether it contains melanoma cells.
If the sentinel node contains melanoma cells, all the lymph glands in the area may be removed – this is known as a block dissection. If the sentinel node does not contain melanoma cells, it is 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 trials, to see how effective it is.
Radiotherapy
Radiotherapy 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 (or fatigue) is also a common side effect of radiotherapy.
These side effects usually decrease gradually once the treatment has ended, but it may take some months for skin changes to go back to normal. A small number of people find that their bowel function is permanently altered. It is important to discuss this with your doctor as it is often possible to find ways of reducing any problems. Your doctor or a dietitian at the hospital can give you further advice.
Chemotherapy
Chemotherapy is the use of anti-cancer drugs to destroy cancer cells. It may be given after surgery as an adjuvant treatment. It may also be given if surgery is not possible or 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 are 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 very 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 range of drinks is 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.
Follow-up
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.
Your feelings
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. It is quite natural, and important, to be able to express them. Each person has their own way of coping with difficult situations; some people find it helpful to talk to friends or family, 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.
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