Merkel Cell Carcinoma

Merkel Cell Carcinoma, also known as cutaneous neuroendocrine carcinoma, is a rare and aggressive form of skin cancer with a high risk for recurring and metastasizing. It occurs almost exclusively in white skin, and is slightly more common in males.


Approximately 80% of examined Merkel cell carcinomas have Merkel cell polyomavirus (MCPyV) identified. It is believed that when immune function is compromised, the virus induces gene alterations that result in Merkel cell cancer.

Because virus-negative tumors typically develop on skin that has been exposed to the sun, they are linked to high UV radiation exposure. One major contributing factor to the development of Merkel cell carcinomas is immunosuppression.

It was once thought that Merkel cells, which are skin pressure receptors, were the source of Merkel cell cancer. Based on clonal immunoglobulin chain rearrangement, early B-cell markers expressed, and cellular shape, a new study suggests that their ancestors were lymphocytes.  

Clinical features:

Typically, asymptomatic, non-tender, solitary, uneven red nodule that is rapidly growing is the first sign of Merkel cell cancer. Although it grows far more quickly, it frequently resembles other, more prevalent skin malignancies in appearance, such as basal cell carcinoma.

Multiple metastases may form surrounding the primary tumor in Merkel cell tumors, which spread through the lymphatic system and can cause a local recurrence. Additionally, it may spread to axillae, groin, and neck lymph nodes.

The rate of recurrence  is markedly higher than that for invasive melanoma, squamous cell carcinoma, or basal cell carcinoma. The majority of recurrences happen in the first two years following diagnosis.


Any tumor exhibiting the following clinical characteristics, which are seen in roughly 90% of patients, should be ruled out as being likely to be Merkel cell carcinoma. These characteristics can be remembered using the acronym “AEIOU”:

  • Asymptomatic or non-tender
  • Expanding rapidly
  • Immune suppressed
  • Older than 50
  • UV-exposed fair skin

A tumor biopsy is the primary test. This demonstrates the typical histology of Merkel cell cancer. Since thyroid transcription factor (TTF1) is typically negative and cytokeratin-20 (CK20) is positive in up to 95% of tumors, immunohistochemistry can be useful.

If the tumor has progressed to other places, a general examination, including assessment of the local lymph nodes, and staging studies may be scheduled. Imaging modalities, lymph mode ultrasound scanning, and sentinel node biopsies are examples of staging investigations. 


Treatment options include excision or Mohs surgery.  Except in very small lesions, radiation therapy is usually administered to the Merkel cell carcinoma site along with regional lymph node placement.

Pembrolizumab and nivolumab, immune checkpoint inhibitors for advanced Merkel cell carcinoma, up to 50% of patients have shown positive response. Avelumab, another PD-1/PD-L1 medication, received expedited approval from the US Food and Drug Administration in March 2017 to treat metastatic Merkel cell carcinoma.


Five-year survival rates are overall 30–50%. Survival rates are better for patients initially diagnosed with Stage 1 Merkel cell carcinoma and in younger patients than when it has already metastasized or patients are over 80 years of age. 

Written by:

Mohammed Alahmadi, Medical Student. 

Revised by:

Maee Barakeh, Medical Student. 



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