Anorectal mucosal melanoma

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 in the bowel or colon area.

Types of anorectal mucosal melanoma

Anorectal melanoma can affect the rectum, anal canal or both. Although, most lesions are located close to the anus.

What are the causes?

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.

Symptoms

The most common symptom of anorectal melanoma is bleeding from the rectum (back passage).

Other possible symptoms include:

  • Pain in the back passage
  • Itching in the back passage
  • Swelling or a lump in the groin area
  • Change in normal bowel habits (diarrhoea, constipation or incontinence)
  • You may feel an urgent need to empty your bowels, although you may not be able to do so.
  • As with other types of melanomas, the area may be pigmented (darker) but this is not always the case.

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.

Anorectal mucosal melanoma: Diagnosis and staging

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.

Staging for anorectal mucosal melanoma

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.

Staging for anorectal melanoma is different from other mucosal melanomas and is often staged as follows:

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

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

Anorectal mucosal melanoma: Treatment

Surgery

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.

Other possible treatments

If the anorectal mucosal melanoma has spread to other parts of your body you may be offered other treatments or the option of taking part in a clinical trial.  For more information on clinical trials, please visit the Melanoma TrialFinder (link)

If you have any questions about your diagnosis or treatment, our specialised Melanoma Helpline nurses are here to support you on 0808 801 0777

References

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