Merkel Cell Carcinoma

Key Points
Rare, aggressive form of skin cancer typically appearing on skin regularly exposed to sun
Likely cause is a combination of ultraviolet radiation from the sun and viral exposure
Consists of a single nodule, red in color, which appears similar to other skin cancers

Merkel cell carcinoma is a rare, aggressive form of skin cancer which typically appears on skin which has been regularly exposed to sunlight. Most lesions occur on the head and neck and up to 50% are found in a periorbital position. It usually consists of a single nodule which is red in color and occasionally ulcerated. Smaller nodules may form around the central nodule, and the condition often metastasizes to other areas, typically the lymphatic system. This may cause the formation of nodules in lymph nodes in the groin, axillae, or neck.

It is thought that the condition is related to exposure to ultraviolet radiation. Additionally, a newly identified virus, Merkel cell polyomavirus, has been found to be present in 80% of tested cases. It is likely that this virus integrates into host DNA, and in conjunction with UV radiation, causes damage to one or more genes encoding tumor suppressor proteins.

Differential Diagnosis (Other conditions with similar appearance)
Basal Cell Carcinoma
Metastatic Carcinoma of the Skin
Dermatofibroma
Squamous Cell Carcinoma
Kaposi Sarcoma
Keratoacanthoma
Malignant Melanoma

Diagnosis
Key Points
Biopsy must be performed to confirm diagnosis and rule out other conditions

Merkel cell carcinoma may be initially suspected based on the appearance of the affected area, but a biopsy will be required to confirm the diagnosis and to rule out other, similar appearing conditions.

Treatment
Surgical excision of the tumor with consideration of sentinel lymph node testing
Referral to oncology is suggested for systemic workup to exclude metastatic disease and to consider chemotherapy and/or radiation.

Treatment of MCC is predicated on the extent of the condition. In cases localized to the affected area, removal via surgical excision is the typical treatment, sometimes followed by a course of radiotherapy. There has been some evidence to suggest that sentinel lymph node testing should be performed during the excision. If the condition has metastasized to the lymph nodes in the affected area, surgical excision of the tumor and lymph nodes and radiotherapy treatment may be accompanied by systemic chemotherapy. Cases which involve distant metastases are difficult to treat and have a poor prognosis. Treatments in this stage of the condition include radiotherapy and/or chemotherapy.