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This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http://cancer.gov or call 1-800-4-CANCER.
Merkel cell carcinoma is a very rare disease in which malignant (cancer) cells form in the skin.
Merkel cells are found in the top layer of the skin. These cells are very close to the nerve endings that receive the sensation of touch. Merkel cell carcinoma, also called neuroendocrine carcinoma of the skin or trabecular cancer, is a very rare type of skin cancer that forms when Merkel cells grow out of control. Merkel cell carcinoma starts most often in areas of skin exposed to the sun, especially the head and neck, as well as the arms, legs, and trunk.
Anatomy of the skin showing the epidermis, dermis, and subcutaneous tissue. Merkel cells are in the layer of basal cells at the deepest part of the epidermis and are connected to nerves.
Merkel cell carcinoma tends to grow quickly and to metastasize (spread) at an early stage. It usually spreads first to nearby lymph nodes and then may spread to lymph nodes or skin in distant parts of the body, lungs, brain, bones, or other organs.
Merkel cell carcinoma is the second most common cause of skin cancer death after melanoma.
Sun exposure and having a weak immune system can affect the risk of Merkel cell carcinoma.
Anything that increases your risk of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn't mean that you will not get cancer. Talk with your doctor if you think you may be at risk. Risk factors for Merkel cell carcinoma include the following:
Merkel cell carcinoma usually appears as a single painless lump on sun-exposed skin.
This and other changes in the skin may be caused by Merkel cell carcinoma or by other conditions. Check with your doctor if you see changes in your skin.
Merkel cell carcinoma usually appears on sun-exposed skin as a single lump that is:
Tests and procedures that examine the skin are used to diagnose Merkel cell carcinoma.
The following tests and procedures may be used:
Certain factors affect prognosis (chance of recovery) and treatment options.
The prognosis and treatment options depend on the following:
Prognosis also depends on how deeply the tumor has grown into the skin.
After Merkel cell carcinoma has been diagnosed, tests are done to find out if cancer cells have spread to other parts of the body.
The process used to find out if cancer has spread to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment.
The following tests and procedures may be used in the staging process:
There are three ways that cancer spreads in the body.
Cancer can spread through tissue, the lymph system, and the blood:
Cancer may spread from where it began to other parts of the body.
When cancer spreads to another part of the body, it is called metastasis. Cancer cells break away from where they began (the primary tumor) and travel through the lymph system or blood.
The metastatic tumor is the same type of cancer as the primary tumor. For example, if Merkel cell carcinoma spreads to the liver, the cancer cells in the liver are actually cancerous Merkel cells. The disease is metastatic Merkel cell carcinoma, not liver cancer.
The following stages are used for Merkel cell carcinoma:
Tumor sizes are often measured in centimeters (cm) or inches. Common food items that can be used to show tumor size in cm include: a pea (1 cm), a peanut (2 cm), a grape (3 cm), a walnut (4 cm), a lime (5 cm or 2 inches), an egg (6 cm), a peach (7 cm), and a grapefruit (10 cm or 4 inches).
Stage 0 (carcinoma in situ)
In stage 0, abnormal Merkel cells are found in the top layer of skin. These abnormal cells may become cancer and spread into nearby normal tissue.
In stage I, the tumor is 2 centimeters or smaller.
Stage II Merkel cell carcinoma is divided into stages IIA and IIB.
Stage III Merkel cell carcinoma is divided into stages IIIA and IIIB.
In stage IIIA, either of the following is found:
In stage IIIB, the tumor may be any size and:
In stage IV, the tumor has spread to skin that is not close to the primary tumor or to other parts of the body, such as the liver, lung, bone, or brain.
Merkel cell carcinoma can recur (come back) after it has been treated.
The cancer may come back in the skin, lymph nodes, or other parts of the body. It is common for Merkel cell carcinoma to recur.
There are different types of treatment for patients with Merkel cell carcinoma.
Different types of treatments are available for patients with Merkel cell carcinoma. Some treatments are standard (the currently used treatment), and some are being tested in clinical trials. A treatment clinical trial is a research study meant to help improve current treatments or obtain information on new treatments for patients with cancer. When clinical trials show that a new treatment is better than the standard treatment, the new treatment may become the standard treatment. Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.
Four types of standard treatment are used:
One or more of the following surgical procedures may be used to treat Merkel cell carcinoma:
After the doctor removes all the cancer that can be seen at the time of the surgery, some patients may be given chemotherapy or radiation therapy after surgery to kill any cancer cells that are left. Treatment given after the surgery, to lower the risk that the cancer will come back, is called adjuvant therapy.
Radiation therapy is a cancer treatment that uses high-energy x-rays or other types of radiation to kill cancer cells or keep them from growing. External radiation therapy uses a machine outside the body to send radiation toward the area of the body with cancer. It is used to treat Merkel cell carcinoma, and may also be used as palliative therapy to relieve symptoms and improve quality of life.
Chemotherapy is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping the cells from dividing. When chemotherapy is taken by mouth or injected into a vein or muscle, the drugs enter the bloodstream and can reach cancer cells throughout the body (systemic chemotherapy).
Immunotherapy is a treatment that uses the patient's immune system to fight cancer. Substances made by the body or made in a laboratory are used to boost, direct, or restore the body's natural defenses against cancer. This cancer treatment is a type of biologic therapy.
Some types of immune cells, such as T cells, and some cancer cells have certain proteins, called checkpoint proteins, on their surface that keep immune responses in check. When cancer cells have large amounts of these proteins, they will not be attacked and killed by T cells. Immune checkpoint inhibitors block these proteins and the ability of T cells to kill cancer cells is increased.
There are two types of immune checkpoint inhibitor therapy:
Immune checkpoint inhibitor. Checkpoint proteins, such as PD-L1 on tumor cells and PD-1 on T cells, help keep immune responses in check. The binding of PD-L1 to PD-1 keeps T cells from killing tumor cells in the body (left panel). Blocking the binding of PD-L1 to PD-1 with an immune checkpoint inhibitor (anti-PD-L1 or anti-PD-1) allows the T cells to kill tumor cells (right panel).
See Drugs Approved for Merkel Cell Carcinoma for more information.
New types of treatment are being tested in clinical trials.
Information about clinical trials is available from the NCI website.
Treatment for Merkel cell carcinoma may cause side effects.
For information about side effects caused by treatment for cancer, see our Side Effects page.
Patients may want to think about taking part in a clinical trial.
For some patients, taking part in a clinical trial may be the best treatment choice. Clinical trials are part of the cancer research process. Clinical trials are done to find out if new cancer treatments are safe and effective or better than the standard treatment.
Many of today's standard treatments for cancer are based on earlier clinical trials. Patients who take part in a clinical trial may receive the standard treatment or be among the first to receive a new treatment.
Patients who take part in clinical trials also help improve the way cancer will be treated in the future. Even when clinical trials do not lead to effective new treatments, they often answer important questions and help move research forward.
Patients can enter clinical trials before, during, or after starting their cancer treatment.
Some clinical trials only include patients who have not yet received treatment. Other trials test treatments for patients whose cancer has not gotten better. There are also clinical trials that test new ways to stop cancer from recurring (coming back) or reduce the side effects of cancer treatment.
Clinical trials are taking place in many parts of the country. Information about clinical trials supported by NCI can be found on NCI's clinical trials search webpage. Clinical trials supported by other organizations can be found on the ClinicalTrials.gov website.
Follow-up tests may be needed.
Some of the tests that were done to diagnose the cancer or to find out the stage of the cancer may be repeated. Some tests will be repeated in order to see how well the treatment is working. Decisions about whether to continue, change, or stop treatment may be based on the results of these tests.
Some of the tests will continue to be done from time to time after treatment has ended. The results of these tests can show if your condition has changed or if the cancer has recurred (come back). These tests are sometimes called follow-up tests or check-ups.
For information about the treatments listed below, see the Treatment Option Overview section.
Treatment of stage I and stage II Merkel cell carcinoma may include the following:
Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.
Treatment of stage III Merkel cell carcinoma may include the following:
Treatment of stage IV Merkel cell carcinoma may include the following:
Treatment of recurrent Merkel cell carcinoma may include the following:
For more information from the National Cancer Institute about Merkel cell carcinoma, see the following:
For general cancer information and other resources from the National Cancer Institute, see the following:
Physician Data Query (PDQ) is the National Cancer Institute's (NCI's) comprehensive cancer information database. The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries come in two versions. The health professional versions have detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions have cancer information that is accurate and up to date and most versions are also available in Spanish.
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Purpose of This Summary
This PDQ cancer information summary has current information about the treatment of merkel cell carcinoma. It is meant to inform and help patients, families, and caregivers. It does not give formal guidelines or recommendations for making decisions about health care.
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A clinical trial is a study to answer a scientific question, such as whether one treatment is better than another. Trials are based on past studies and what has been learned in the laboratory. Each trial answers certain scientific questions in order to find new and better ways to help cancer patients. During treatment clinical trials, information is collected about the effects of a new treatment and how well it works. If a clinical trial shows that a new treatment is better than one currently being used, the new treatment may become "standard." Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.
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The best way to cite this PDQ summary is:
PDQ® Adult Treatment Editorial Board. PDQ Merkel Cell Carcinoma Treatment. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/skin/patient/merkel-cell-treatment-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389202]
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Last Revised: 2021-06-25
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