Merkel cell carcinoma

Merkel cell carcinoma is a rare type of non-melanoma skin cancer. It starts in Merkel cells, which are found in the deepest part of the top or outer layer of skin (epidermis) and in the hair follicles (small sacs where hair starts to grow). Merkel cells are close to nerves and help give the sense of touch. They also make hormones.

Merkel cell carcinoma usually starts on areas of skin exposed to the sun, especially the head, neck, arms and legs. It grows and spreads quickly (is aggressive).

Merkel cell carcinoma is also called neuroendocrine cancer of the skin or trabecular carcinoma.

Signs and symptoms

Merkel cell carcinoma usually appears as a firm and raised lump on the skin. The lump can be red or purple and it is not usually painful.

Since Merkel cell carcinoma tends to grow and spread quickly, new lumps may form on nearby skin. Lymph nodes may also become larger than normal, especially in the neck or under an arm.


The tests used to diagnose Merkel cell carcinoma usually include a physical exam, skin exam and skin biopsy of the lump. The skin biopsy is done using a shave biopsy, punch biopsy, incisional biopsy or excisional biopsy. If Merkel cell carcinoma is diagnosed, then other tests, such as a CT scan and an MRI, may be done to check if the cancer has spread to other parts of the body. You may also be offered a sentinel lymph node biopsy. This test can give the doctor information about how quickly the cancer is growing and spreading and will help plan treatment.

Find out more about these tests and diagnosis of non-melanoma skin cancer.


Staging describes or classifies a cancer based on how much cancer there is in the body and where it is when first diagnosed. This is often called the extent of cancer. Information from tests is used to find out the size of the tumour, which parts of the skin have cancer, whether the cancer has spread from where it first started and where the cancer has spread. Your healthcare team uses the stage to plan treatment and estimate the outcome (your prognosis).

The staging system used for Merkel cell carcinoma is the TNM system. For Merkel cell carcinoma there are 5 stages – stage 0 followed by stages 1 to 4. Often the stages 1 to 4 are written as the Roman numerals I, II, III and IV. Generally, the higher the stage number, the more the cancer has spread. Talk to your doctor if you have questions about staging.

Find out more about staging cancer.

Merkel cell carcinoma is staged differently than other non-melanoma skin cancers.

Stage 0 (carcinoma in situ)

The cancer is only in the top or outer layer of the skin (epidermis).

Stage 1

The cancer is 2 cm or smaller.

Stage 2A

The cancer is larger than 2 cm.

Stage 2B

The cancer may have spread to nearby bone, muscle, cartilage or fascia (connective tissue that wraps around muscles, nerves, blood vessels and organs).

Stage 3A

The cancer has spread to nearby lymph nodes.

Stage 3B

There are areas of cancer between where the cancer started (primary site) and the closest lymph nodes (called in-transit metastasis). It may also have spread to nearby lymph nodes.

Stage 4

The cancer has spread to other parts of the body (called distant metastasis), such as tissues under the skin or lymph nodes farther from where the cancer started, the lungs or the liver. This is also called metastatic cancer.

Recurrent Merkel cell carcinoma

Recurrent Merkel cell carcinoma means that the cancer has come back after it has been treated. If it comes back in the same place that the cancer first started, it’s called local recurrence. If it comes back in tissues or lymph nodes close to where it first started, it’s called regional recurrence. It can also recur in another part of the body. This is called distant metastasis or distant recurrence.

Treatments for Merkel cell carcinoma

You may be offered one or more of the following treatments for Merkel cell carcinoma. Your healthcare team will suggest treatments based on the stage and where the cancer started. They will work with you to develop a treatment plan.


The type of surgery done depends on the stage (the size of the cancer and where it is).

Wide local excision removes the cancer along with some normal tissue around it (called the surgical margin). It is the standard type of surgery used when the Merkel cell carcinoma is only in the skin and has not spread to other parts of the body.

Mohs surgery removes the cancer in layers, little by little, until no cancer remains. It may be done when doctors want to leave as much normal tissue as possible (called tissue sparing). For example, Mohs surgery may be done for Merkel cell carcinoma on the face.

Lymph node dissection removes lymph nodes that may contain cancer. It is done when the doctor can feel enlarged lymph nodes or the sentinel lymph node biopsy shows that the sentinel lymph node contains cancer. A lymph node dissection can be done after the primary tumour has been removed.

Radiation therapy

External beam radiation therapy uses a machine to direct a beam of radiation to the cancer and some of the tissue around it.

Radiation therapy can be used after surgery to destroy any remaining cancer cells and help reduce the risk of the cancer coming back, or recurring (called adjuvant therapy). Sometimes the radiation is directed toward nearby lymph nodes. It can also be used to treat Merkel cell carcinoma that has come back after surgery. Radiation therapy may be used to relieve symptoms of advanced Merkel cell carcinoma (called palliative therapy).

Chemotherapy and other drugs

Chemotherapy uses drugs to treat Merkel cell carcinoma. It is most often used to treat stage 4 Merkel cell carcinoma to help shrink the cancer, to slow the growth and spread of the cancer and to relieve symptoms. It may be given alone or with other treatments.

The most common chemotherapy treatment for Merkel cell carcinoma is cisplatin (Platinol AQ) or carboplatin (Paraplatin, Paraplatin AQ), which may be combined with etoposide (Vepesid, VP-16). Topotecan (Hycamtin) may be used alone in some cases, such as for older people. Chemotherapy is usually given with a needle into a vein (intravenously) every few weeks. Treatment usually continues as long as the cancer doesn’t grow or spread any farther and you can cope with the side effects.

Avelumab (Bavencio) is a monoclonal antibody drug that may be used to treat metastatic Merkel cell carcinoma. It works by helping immune system cells attack and kill cancer cells. It is given through a needle into a vein (intravenous infusion) once every 2 weeks. Your doctor will decide how many treatments you need.

Clinical trials

You may be asked if you want to join a clinical trial for skin cancer. Find out more about clinical trials.

Expert review and references

  • American Joint Committee on Cancer. AJCC Cancer Staging Handbook. 7th ed. Chicago: Springer; 2010.
  • Brierley JD, Gospodarowicz MK, Wittekind C (eds.). TNM Classification of Malignant Tumours. 8th ed. Wiley Blackwell; 2017.
  • Christensen SR, Leffell DJ . Cancer of the skin. DeVita VT Jr, Lawrence TS, Rosenberg SA. Cancer: Principles and Practice of Oncology. 10th ed. Wolters Kluwer Health/Lippincott Williams & Wilkins; 2015: 92:1314-1336.
  • Drugs and Health Products, Health Canada. Regulatory Decision Summary: Bavencio. 2017:
  • National Cancer Institute. Merkel Cell Carcinoma Treatment for Health Professionals (PDQ®). 2015:
  • National Cancer Institute. Merkel Cell Carcinoma Treatment (PDQ®). 2015:
  • National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Merkel Cell Carcinoma (Version 1.2016). 2016.
  • Peters S, Olencki T . Unusual cutaneous malignancies. Raghavan D, Blanke CD, Honson DH, et al (eds.). Textbook of Uncommon Cancer. 4th ed. Wiley Blackwell; 2012: 49:667-684.

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