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Merkel cell carcinoma

Merkel cell carcinoma of the skin is a rare form of skin cancer. It is 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.

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 is also associated with the development of Merkel cell carcinomas.

A new virus, Merkel cell polyomavirus, has been detected in 8 out of 10 Merkel cell carcinomas tested (January 2008).

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

Image supplied by Catherine Skiens

What is the treatment?

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. 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.

Disease involving regional lymph nodes
If the cancer has spread to involve the lymph nodes, then these may be surgically removed 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.