Anorectal mucosal melanoma affects the areas in and around the anus, or the rectal cavity. It is very rare, and the signs and symptoms of anorectal mucosal melanoma are similar to other cancers and conditions in the bowel or colon area.
Anorectal melanoma can affect the rectum, anal canal or both. Although, most lesions are located close to the anus.
The causes of anorectal mucosal melanoma (sometimes abbreviated to AMM or ARMM) remain largely unknown. It may be a combination of age, genetics and environmental factors. It tends to occur more frequently in individuals over the age of 50, and is more common in women.
The most common symptom of anorectal melanoma is bleeding from the rectum (back passage).
Other possible symptoms include:
The symptoms are often similar to other symptoms of cancer in the colon, or bowel area. However, some less serious conditions like haemorrhoids, or polyps can also result in some of the symptoms listed. It is therefore important to arrange an early appointment with your GP, so relevant action can be taken fast.
If your GP cannot find another cause for these symptoms, you should be referred quickly (normally within about two weeks) to a clinic, in a specialist hospital for tests and further evaluation. This may involve and appointment with a colorectal surgeon.
It is important that you see your GP if you have symptoms or any ongoing unexplained symptoms that are worrying you. Your GP will examine you which will usually involve feeling your tummy (abdomen) and they may also look for any abnormalities (such as lumps of swellings) in your back passage (rectum). This procedure is called a rectal examination which may be uncomfortable but shouldn’t be painful. Your GP may also feel your groin area for any swollen lymph nodes.
If your GP has any concerns or if they are not sure what the problem is, they will refer you to a hospital specialist who will examine you again and will arrange for you to have a biopsy. This is a small sample of the tissue that will be removed under local anaesthetic to look for cancer cells. It is then analysed by a pathologist (a specialised doctor who diagnoses diseases from tissue and cells in the body) to determine whether it is a melanoma or not. It typically takes a few weeks to receive the results of your biopsy and this can be a very anxious time. You may have other tests to help diagnose anorectal melanoma and these tests can also be used to check whether your anorectal melanoma has spread to other parts of your body.
After a diagnosis of anorectal mucosal melanoma, your medical team will work out the ‘stage’. The stage is a way of describing the key features of your melanoma and is helpful in guiding the best treatment and follow-up for you. Your stage provides an indication of how advanced your melanoma is. Generally, the higher the stage, the more advanced it is.
For most melanomas of the skin (cutaneous melanoma), doctors use an internationally recognised staging system called the TNM system. This system is developed by organisations such as the American Joint Committee on Cancer ( AJCC). It describes the tumour (T), whether cancer has spread to nearby lymph nodes (N), and whether it has spread to other parts of the body (M, metastasis).
However, there is currently no internationally agreed staging system specifically for anorectal mucosal melanoma. For this reason, doctors should still record the tumour using similar TNM terms, as this helps ensure important clinical information is captured consistently.
Since there is no agreed staging system, anorectal mucosal melanoma is often staged using the Ballantyne staging system:
Stage 1 = the melanoma is ‘localised’ which means it is only in the anus and rectum and it has not spread anywhere else
Stage 2 = the melanoma has spread to nearby lymph nodes (AJCC equivalent staging for cutaneous melanoma would be Stage 3)
Stage 3 = the melanoma has spread to other parts of the body (metastasised) – the most common location for spread is the liver for anorectal melanoma (AJCC equivalent staging for cutaneous melanoma would be stage 4)
The main treatment for an anorectal mucosal melanoma is surgery. This should be done by a surgeon who is very experienced in complex colorectal surgery. This is often in a specialised centre where there would be support from an experienced cancer team.
In planning the operation, the medical team will consider the stage of your anorectal mucosal melanoma, your general health and how the surgery may affect your quality of life.
In some situations, you may be offered immunotherapy or a targeted therapy after the surgery. This is known as adjuvant treatment and is given to reduce the risk of the mucosal melanoma coming back. In some cases, immunotherapy may be given before surgery (known as neoadjuvant treatment). Your specialist cancer team will discuss whether these treatments may be suitable for you.
If the anorectal mucosal melanoma has spread to other parts of your body you may be offered other treatments such as immunotherapy, targeted therapy or the option of taking part in a clinical trial.
For more information on immunotherapy treatment, click here.
For more information on targeted therapy, click here.
For more information on clinical trials, please visit the Melanoma TrialFinder.
If you have any questions about your diagnosis or treatment, our specialised Melanoma Helpline nurses are here to support you on
Carvajal RD, Spencer SA, Lydiatt W. Mucosal Melanoma: A Clinically and Biologically Unique Disease Entity. J Natl Compr Canc Netw (2012) 10(3):345–56. doi: 10.6004/jnccn.2012.0034
Malaguarnera G, Madeddu R, Catania VE, et al. Anorectal mucosal melanoma. Oncotarget. 2018;9(9):8785-8800. Published 2018 Jan 2. doi:10.18632/oncotarget.23835
Surgery for anorectal melanoma https://www.macmillan.org.uk/cancer-information-and-support/treatments-and-drugs/surgery-for-anorectal-melanoma
