Key Points for This Section

Merkel cell carcinoma is a very rare disease in which malignant (cancer) cells form in the skin. Sun exposure and having a weak immune system can affect the risk of developing Merkel cell carcinoma. Merkel cell carcinoma usually appears as a single painless lump on sun-exposed skin. Tests and procedures that examine the skin are used to detect (find) and diagnose Merkel cell carcinoma. Certain factors affect prognosis (chance of recovery) and treatment options.

Merkel cell carcinoma is a very rare disease in which malignant (cancer) cells form in the skin.

Merkel cells are hormone -making cells 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, is a very rare type of skin cancer that develops when Merkel cells grow out of control. Merkel cell carcinoma starts most often in areas of skin exposed to the sun, such as the head, neck, arms, and legs.

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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 spreads first to nearby lymph nodes and then may spread to the liver, bone, lungs, brain, or other parts of the body.

Sun exposure and having a weak immune system can affect the risk of developing Merkel cell carcinoma.

Risk factors include the following:

• Being exposed to a lot of natural sunlight.
• Being exposed to artificial sunlight, such as during treatment for psoriasis.
• Having an immune system weakened by disease, such as HIV infection.
• Taking drugs that make the immune system less active, such as after an organ transplant.
• Having a history of other types of skin cancer, such as basal cell or squamous cell cancer.
• Being older than 70 years, male, or white.

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. Other conditions may cause the same symptoms. A doctor should be consulted if changes in the skin are seen.

Merkel cell carcinoma usually appears on sun-exposed skin as a single lump that is:

• Fast-growing.
• Painless.
• Firm and dome-shaped or raised.
• Red or violet in color.

Tests and procedures that examine the skin are used to detect (find) and diagnose Merkel cell carcinoma.

The following tests and procedures may be used:

• Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
• Full-body skin exam: A doctor or nurse checks the skin for bumps or spots that look abnormal in color, size, shape, or texture. The size, shape, and texture of the lymph nodes will also be checked.
• Biopsy: The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer. To diagnose Merkel cell carcinoma, cells are treated with a special stain and viewed with an electron microscope.

Certain factors affect prognosis (chance of recovery) and treatment options.

The prognosis (chance of recovery) and treatment options depend on the following:

• The stage of the cancer (the size of the tumor and whether it has spread to the lymph nodes or other parts of the body).
• Where the cancer is in the body.
• Whether the cancer has just been diagnosed or has recurred (come back).
• The patient's age and general health.

Prognosis also depends on how deeply the tumor has grown into the skin.

Glossary Terms

Not normal. An abnormal lesion or growth may be cancerous, premalignant (likely to become cancer), or benign.

A type of skin cancer that arises from the basal cells, small round cells found in the lower part (or base) of the epidermis, the outer layer of the skin.

The removal of cells or tissues for examination by a pathologist. The pathologist may study the tissue under a microscope or perform other tests on the cells or tissue. There are many different types of biopsy procedures. The most common types include: (1) incisional biopsy, in which only a sample of tissue is removed; (2) excisional biopsy, in which an entire lump or suspicious area is removed; and (3) needle biopsy, in which a sample of tissue or fluid is removed with a needle. When a wide needle is used, the procedure is called a core biopsy. When a thin needle is used, the procedure is called a fine-needle aspiration biopsy.

A term for diseases in which abnormal cells divide without control. Cancer cells can invade nearby tissues and can spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord.

Cancer that begins in the skin or in tissues that line or cover internal organs.

The individual unit that makes up the tissues of the body. All living things are made up of one or more cells.

The process of identifying a disease, such as cancer, from its signs and symptoms.

Any substance, other than food, that is used to prevent, diagnose, treat or relieve symptoms of a disease or abnormal condition. Also refers to a substance that alters mood or body function, or that can be habit-forming or addictive, especially a narcotic.

A microscope (device used to magnify small objects) that uses electrons (instead of light) to produce an enlarged image. An electron microscope shows tiny details better than any other type of microscope.

The cause of acquired immunodeficiency syndrome (AIDS). Also called human immunodeficiency virus.

One of many chemicals made by glands in the body. Hormones circulate in the bloodstream and control the actions of certain cells or organs. Some hormones can also be made in the laboratory.

The complex group of organs and cells that defends the body against infections and other diseases.

Invasion and multiplication of germs in the body. Infections can occur in any part of the body and can spread throughout the body. The germs may be bacteria, viruses, yeast, or fungi. They can cause a fever and other problems, depending on where the infection occurs. When the body’s natural defense system is strong, it can often fight the germs and prevent infection. Some cancer treatments can weaken the natural defense system.

A large organ located in the upper abdomen. The liver cleanses the blood and aids in digestion by secreting bile.

One of a pair of organs in the chest that supplies the body with oxygen, and removes carbon dioxide from the body.

A rounded mass of lymphatic tissue that is surrounded by a capsule of connective tissue. Lymph nodes filter lymph (lymphatic fluid), and they store lymphocytes (white blood cells). They are located along lymphatic vessels. Also called lymph gland.

A rare type of cancer that forms on or just beneath the skin, usually in parts of the body that have been exposed to the sun. It is most common in older people and in people with weakened immune systems. Also called neuroendocrine carcinoma of the skin and trabecular cancer.

To spread from one part of the body to another. When cancer cells metastasize and form secondary tumors, the cells in the metastatic tumor are like those in the original (primary) tumor.

A bundle of fibers that receives and sends messages between the body and the brain. The messages are sent by chemical and electrical changes in the cells that make up the nerves.

Having to do with the interactions between the nervous system and the endocrine system. Neuroendocrine describes certain cells that release hormones into the blood in response to stimulation of the nervous system.

A health professional trained to care for people who are ill or disabled.

A part of the body that performs a specific function. For example, the heart is an organ.

A doctor who identifies diseases by studying cells and tissues under a microscope.

An exam of the body to check for general signs of disease.

The likely outcome or course of a disease; the chance of recovery or recurrence.

A chronic disease of the skin marked by red patches covered with white scales.

To become well and healthy again.

To come back or to return.

Something that may increase the chance of developing a disease. Some examples of risk factors for cancer include age, a family history of certain cancers, use of tobacco products, certain eating habits, obesity, lack of exercise, exposure to radiation or other cancer-causing agents, and certain genetic changes.

Cancer that forms in tissues of the skin. There are several types of skin cancer. Skin cancer that forms in melanocytes (skin cells that make pigment) is called melanoma. Skin cancer that forms in basal cells (small, round cells in the base of the outer layer of skin) is called basal cell carcinoma. Skin cancer that forms in squamous cells (flat cells that form the surface of the skin) is called squamous cell carcinoma. Skin cancer that forms in neuroendocrine cells (cells that release hormones in response to signals from the nervous system) is called neuroendocrine carcinoma of the skin. Most skin cancers form in older people on parts of the body exposed to the sun or in people who have weakened immune systems.

Cancer that begins in squamous cells, which are thin, flat cells that look like fish scales. Squamous cells are found in the tissue that forms the surface of the skin, the lining of the hollow organs of the body, and the passages of the respiratory and digestive tracts. Also called epidermoid carcinoma.

The extent of a cancer in the body. Staging is usually based on the size of the tumor, whether lymph nodes contain cancer, and whether the cancer has spread from the original site to other parts of the body.

An indication that a person has a condition or disease. Some examples of symptoms are headache, fever, fatigue, nausea, vomiting, and pain.

A group or layer of cells that work together to perform a specific function.

A surgical procedure in which tissue or an organ is transferred from one area of a person’s body to another area, or from one person (the donor) to another person (the recipient).

An abnormal mass of tissue that results when cells divide more than they should or do not die when they should. Tumors may be benign (not cancerous), or malignant (cancerous). Also called neoplasm.