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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Merkel cell carcinoma

Merkel cell carcinoma of the skin is a rare form of skin cancer. It may be very aggressive, and often metastasises (spreads) to other parts of the body. It is believed to arise from Merkel cells, which are pressure receptors in the skin. It has an estimated incidence of 0.23 per 100,000 people in caucasian populations. Merkel cell carcinoma is more common in the elderly, with most cases occuring after the age of 50. It is slightly more common in men, and occurs on parts of the body commonly exposed to sunlight, most often the head and neck.

What causes Merkel cell carcinoma?

Ultraviolet radiation has been implicated as a factor in developing Merkel cell carcinoma, due to the occurrence of the tumour on sun exposed skin. Immunosuppression following organ transplantation and other immune deficiency states are also associated with the development of Merkel cell carcinomas.

Merkel cell polyomavirus (MCPyV) has been detected in about 80% Merkel cell carcinomas tested. It is thought that the virus causes gene mutations leading to Merkel cell carcinoma when immune function is defective.

How does it present?

Merkel cell carcinomas usually present as solitary red nodules, and are often similar in appearance to other more common skin cancers. As a result the diagnosis of Merkel cell carcinoma is usually made after a biopsy is taken.

Merkel cell cancers spread through the lymphatic system and multiple smaller seedlings can develop around the main tumour. Later, Merkel cell carcinoma may spread to lymph nodes in the neck, axillae and groin.

Merkel cell carcinoma
Image supplied by Bob Rossborough
Merkel cell carcinoma
Image supplied by Catherine Skiens
Merkel cell carcinoma
Merkel cell carcinoma Merkel cell carcinoma
Image supplied by Dr Slavko Doslo
Merkel cell carcinoma
Also, lower lid: squamous cell carcinoma
Merkel cell carcinoma

What tests should be done?

The main test is excision biopsy of the tumour. This shows characteristic Merkel cell carcinoma pathology. After general examination, including evaluation of local lymph nodes, staging imaging investigations may be arranged to determine whether the tumour has spread ot other sites.

What is the treatment of Merkel cell carcinoma?

Localised disease
For a cancer which is in the early stages and is localised to the skin, surgical excision and radiotherapy are often used as primary treatment. Usually a wide area surrounding the cancer is surgically excised and the site is then treated with radiotherapy post-operatively. Radiation treatment leads to increased local and regional disease control and higher long-term survival rates.

The relevant lymph nodes may also be surgically removed or irradiated as a prophylactic measure. In some cases the relevant lymph nodes may be sampled using a sentinel lymph node biopsy. This helps in staging the tumour but may not influence outcome.

Disease involving regional lymph nodes
If the cancer has spread to involve the lymph nodes, then these may be surgically removed and/or treated with radiotherapy. In some cases systemic chemotherapy may also be administered.

Distant metastatic disease
Distant disease is very serious and has a very poor prognosis. Treatment of metastatic disease is aimed at improving quality of life. In some cases radiotherapy and/or systemic chemotherapy may be administered for treatment.

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Author: Mathew Ludgate MBChB, Dept of Dermatology Greenlane Hospital Auckland

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