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Merkel cell carcinoma

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Merkel cell carcinoma

Also known as trabecular cell carcinoma of the skin, primary neuroendocrine carcinoma of the skin

What is Merkel cell carcinoma?

Merkel cell carcinoma is a very uncommon type of aggressive skin cancer.  It presents most commonly in elderly fair-skinned individuals, particularly in sun-exposed areas on the head, neck and limbs.  It occurs in equal numbers in males and females.  In a small number of people, it is only diagnosed after it has already spread to a lymph node or another part of the body, without an initial skin lesion being detected.

What causes Merkel cell carcinoma?

A virus called the Merkel cell polyomavirus is now thought to be a major factor in the development of this skin cancer.  This virus has been found in up to 80% of Merkel cell carcinomas.  Decreased immune function is also thought to play a role in the development of this form of cancer.  This is why these skin cancers occur more frequently in people who are older or have had organ transplants or in people with human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS).  It is also seen in some individuals with chronic lymphocytic leukaemia.

Sun damage is also thought to play an important role in the development of Merkel cell carcinoma.

What does Merkel cell carcinoma look like?

Merkel cell carcinoma usually presents as a reddish to purplish lump which grows quickly.  It is non-tender and in most cases produces no other symptoms.

Merkel cell carcinoma
Image reproduced with permission of Dr Brian De’Ambrosis


Merkel cell carcinoma
Image reproduced with permission of Dr Brian De’Ambrosis

How is Merkel cell carcinoma diagnosed?

Merkel cell carcinoma is often difficult to diagnose because it can look like other more common skin cancers and cysts.  If there is any doubt about the diagnosis, a sample (biopsy) of the lump is taken to confirm the diagnosis under a microscope.

Once a Merkel cell carcinoma has been diagnosed, the dermatologist will thoroughly examine the skin for other skin cancers and any sign that this cancer has spread.  This is done by a clinical examination of the lymph nodes and abdomen and through PET (position emission topography) and CT (computed tomography) scans.

How is Merkel cell carcinoma treated?

Merkel cell carcinoma is usually treated with surgery. The surgery removes the cancer as well as a margin of normal skin around the edge of the skin cancer.  Depending on the position of the Merkel cell carcinoma, a special test might be done which involves investigating the draining lymph nodes for spreading of the cancer (sentinel node biopsy).  Radiotherapy is nearly always part of the treatment.

Chemotherapy is generally only used if the Merkel cell carcinoma has already spread away from the first site where it was found.

What follow up is required?

People who have had a Merkel cell carcinoma will generally see their dermatologist every 3 to 6 months in the first 2 years and then every 6 to 12 months after that.  Regular full skin examinations are necessary to check for new cancers and monitor for signs of spread of the Merkel cell carcinoma.

What is the likely outcome of Merkel cell carcinoma?

The prognosis for Merkel cell carcinoma is poor. Unfortunately the condition frequently spreads. 30-50% of patients die from the disease having spread to other parts of the body.  The overall 5-year survival rate is 40% and relative survival rate (compared with age and sex match population data) is 54%. Those who have small, localised tumours of less than 2 cm in diameter have a better prognosis than those whose disease has spread to local lymph nodes or other organs.

Future developments

Researchers are investigating the genetics of the Merkel cell polyomavirus so that treatments may be better tailored to the individual’s prognosis.

This information has been written by Dr Brian De’Ambrosis

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