Definition and Overview
Merkel cell carcinoma (MCC) is a rare type of skin cancer. It is very uncommon, affecting only 2,000 people in the United States. However, it is often aggressive and life-threatening. It spreads to the lymph nodes and distant sites fast. Its recurrence rate is also high, especially for patients with bigger tumours.
MCC occurs when Merkel cells grow uncontrollably. Also known as tactile epithelial cells, these oval-shaped skin cells are found on the uppermost layer of the skin. They are also near nerve endings and are believed to promote touch sensation.
MCC can affect anyone, but it is more common among older people. Those who have a weakened immune system are also vulnerable to the condition.
This skin cancer does not have any cure. But it is treatable and manageable. The survival rate is high and the prognosis is good when caught early. For those with stage IA cancer, the 5-year survival rate is 80%. However, this number drops to just 20% when cancer reaches stage IV. By then, the disease has already spread to distant organs, such as the brain and the liver.
Causes of Condition
Like other forms of cancer, the causes of Merkel cell carcinoma are unknown. Factors that are believed to increase one’s risk of the condition are the following:
Long-term sun exposure - MCC usually affects the parts of the body commonly exposed to the sun. These include the head, hands, and arms.
Tanning bed exposure - People who often use tanning beds are also at risk. These beds mimic the effects of sunlight on the skin.
Skin colour - In general, those with lighter skin are more prone to all types of skin cancer. These people have less melanin, which helps reduce the effects of UV rays on the skin.
Certain types of virus - Some studies suggest a link between MCC and a benign virus called merkel cell polyomavirus. The virus is found in up to 80% of all MCC cases. It can stay in the body without causing symptoms. How it increases the risk of MCC is yet to be determined.
Old age - Older people are at risk of MCC because of their weaker immune system. The condition is common in people 50 years and older.
Skin cancer history - People who have had other types of skin cancers are more prone of developing MCC.
Gender - The disease is more common among men than women.
Merkel cell carcinoma appears as a painless bump on the skin. It is often firm and has bluish or red-purple colour. It is usually not dark or brown in colour like melanoma. It is also not scaly or rough like squamous cell carcinoma. It does not have skin colour on its borders. Its characteristics make it easier for specialists to easily recognise it.
The bump can appear on various parts of the body. These include commonly hidden areas, such as the buttocks. But they are more common on sun-exposed parts. They can also develop on the scalp.
The bump can grow quickly in a short time. This rapid growth is often the reason why patients seek medical attention.
Who to See and Types of Treatments Available
People with suspicious bumps must consult a skin specialist (dermatologist) right away. To assess the condition, the doctor will obtain the patient’s medical history and carry out a standard physical exam.
An important step in diagnosing MCC is a skin biopsy. In this procedure, the doctor obtains a skin sample for analysis. The test can determine if the bump is benign or malignant. The test also helps doctors determine the type of cancer the patient has if the tumour is found to be malignant. The test also helps rule out other forms of skin problems. This is important because it allows doctors to determine the most appropriate treatment for the patient.
In up to 85% of cases, the cancer presents as a primary lesion. This means that it is evident on the skin. In some cases, MCC is discovered in the lymph nodes. Thus, the doctor may also check the lymph nodes and observe their size and texture.
Treatment options for MCC are the following:
Surgery - Surgery to treat MCC involves excising the tumour and about 2 centimeters of the skin surrounding it. A sentinel lymph node biopsy can also be performed during surgery. This procedure can confirm if cancer has spread to the lymph nodes. Depending on the results of the test, the affected lymph nodes may also be removed.
Radiation therapy - This therapy can be carried out to ensure that no cancer cells remain following surgery. It is also considered as the primary or only treatment for people who are not well enough to undergo invasive procedures.
Chemotherapy - This is recommended when resection is no longer an option or when cancer has already spread to distant parts of the body. It may involve the use of one or more types of drugs designed to remove, kill, or damage cancer cells.
Immunotherapy - This treatment is designed to boost the immune system so it can better fight cancer. So far, one drug has been approved. It is called avelumab. It is meant for patients 12 years old and above. It can be used by people who do not respond very well to chemotherapy.
Merkel cell carcinoma. Fort Washington, Pa.: National Comprehensive Cancer Network. http://www.nccn.org/professionals/physician_gls/f_guidelines.asp. The American Cancer Society. https://www.cancer.org/cancer/merkel-cell-skin-cancer.html
Kwun HJ, Shuda M, Feng H, Camacho CJ, Moore PS, Chang Y. Merkel cell polyomavirus small T antigen controls viral replication and oncoprotein expression by targeting the cellular ubiquitin ligase SCFFbw7. Cell Host Microbe. 2013 Aug 14. 14(2):125-35