1. What is Merkel cell carcinoma?

Merkel cell carcinoma (MCC) is a rare, aggressive type of skin cancer that forms on or just under the skin. It is also called primary small cell carcinoma of the skin, trabecular carcinoma, APUDoma, neuroendocrine carcinoma, endocrine carcinoma, or primary undifferentiated tumor of the skin (1). MCC is believed to start in neuroendocrine cells called Merkel cells. These cells release hormones into the blood when stimulated by the nervous system. They migrate from part of the nervous system called the neural crest to the skin (2). Merkel cells are believed to play a role in making the skin sensitive to touch (3).

2. How often does Merkel cell carcinoma occur?

Approximately 1,200 new cases of MCC are diagnosed in the United States each year (4), compared with almost 60,000 new cases of melanoma and more than 1 million new cases of nonmelanoma skin cancer. The incidence of MCC has been rising, with a 3-fold increase between 1986 and 2001 (4). Most patients diagnosed with MCC are over age 50 at diagnosis (the average age is 69), with only 5 percent of cases diagnosed in those under age 50 (5). MCC is more common in white people than in other racial/ethnic groups. Some cases have been reported in Japanese people, but very few have been seen in black people (6).

3. What are the possible causes of Merkel cell carcinoma?

The exact cause of MCC is unknown, but it appears to be linked to sun exposure and immunosuppression (suppression of the body's immune system and its ability to fight infections or disease) (2). Sun exposure as a risk factor for MCC is supported by data that show a rise in incidence corresponding with the solar UVB index (scale indicating the intensity of solar ultraviolet-B (UVB) radiation at noon for a particular location) (6). MCC has been linked to conditions such as HIV infection, chronic lymphocytic leukemia, Hodgkin lymphoma (cancer of the lymph system), ectodermal dysplasia (a disease involving abnormal tissue development), and Cowden disease (a disease in which masses of abnormal but benign tissues grow in multiple sites in the body). Other possible causes include exposure to arsenic and treatment for psoriasis that uses psoralens (a medication that causes the skin to become sensitive to light) and ultraviolet-A light (PUVA) (2).

4. What are the symptoms of Merkel cell carcinoma?

The most common symptom of any skin cancer, including MCC, is a change in the skin, especially a change in an existing mole or a new growth. MCC appears as a firm, painless lump within the skin that may resemble a cyst but is fixed; i.e., cannot be moved. The lump is usually less than 2 cm (about ¾ inch) in size and can be red, pink, or blue-violet. MCC is different from other skin cancers in that it grows rapidly over a few weeks or months (5).

5. Where does Merkel cell carcinoma develop?

MCC is usually found on sun-exposed areas of the body. Fifty percent of cases occur on the head and neck, especially around the eye and on the eyelid (1). Forty percent of cases occur on the arms and legs (2). MCC has also been found on the trunk and other areas of the skin that are not usually exposed to the sun (1).

6. How is Merkel cell carcinoma diagnosed and staged?

The doctor may use the following procedures and tests to diagnose MCC. Some of these tests are also used to help determine the stage of the disease. Stage is a description of the extent of cancer.

• A biopsy is the removal of cells or tissue from a tumor for examination by a pathologist. The pathologist may study tissue samples under a microscope or perform other tests on the cells or tissue. Biopsies are used for both diagnosis and staging. The surgeon may also remove lymph nodes (small, round organs that trap cancer cells, bacteria, or other harmful substances) to help determine the stage of the disease.
  
  
• Sentinel lymph node (SLN) biopsy is a procedure in which the sentinel lymph node is removed and examined under a microscope to determine whether cancer cells are present. The sentinel lymph node is the first lymph node to which cancer is likely to spread from the primary tumor. SLN biopsy is used to help determine the stage of the disease. SLN biopsy may cause fewer side effects than standard lymph node removal because fewer lymph nodes are taken out.
  
  
• Immunohistochemistry (staining of cells with agents that react with antibodies on the surface of cancer cells) is a laboratory technique used to tell the difference between MCC and other types of cancer (2).
  
  
• Computed tomography (CT), a procedure that uses special x-ray equipment to obtain cross-sectional pictures of the body, can distinguish MCC from small cell lung cancer and show whether the disease has metastasized (spread) to other parts of the body (5).
  
  
• In an octreotide scan (sometimes called Somatostatin Receptor Scintigraphy or SRS), the doctor injects a small amount of a radioactive drug into a vein. The drug travels through the bloodstream and attaches to tumor cells. A machine called a scanner detects the radioactive material and creates scans (pictures) showing where the tumor cells are located in the body. For MCC, this test can be used for both diagnosis and staging (5).
  
  
• A PET scan uses radioactive sugar, which is absorbed by cancer cells and appears as dark areas on the scan. It can be used for both diagnosis and staging of MCC.
  
  
7. How is Merkel cell carcinoma treated?

Surgery is the most common treatment for MCC. Surgery with wide margins (a large border of healthy tissue removed with the tumor) is the recommended treatment for MCC. Mohs micrographic surgery, a technique in which individual layers of tissue are removed and examined under a microscope until all cancerous tissue has been removed, may be used instead of traditional surgery with wide margins. Mohs micrographic surgery may be a good alternative for MCC tumors on highly visible areas such as the face, and in areas where the surgeon would not be able to obtain wide margins (5).

The surgeon may remove lymph nodes to help stage the disease or to prevent recurrence (cancer coming back). The patient may also receive adjuvant radiation therapy (treatment given after the primary therapy) to decrease the chance of recurrence. Chemotherapy is the usual treatment if the disease has spread beyond the lymph nodes to areas that are not treatable by radiation therapy.

Supportive care is treatment given to improve the quality of life of patients who have a serious or life-threatening disease, such as cancer. It prevents or treats as early as possible the symptoms of the disease, side effects caused by treatment of the disease, and psychological, social, and spiritual problems related to the disease or its treatment. For example, anticancer drugs such as carboplatin and etoposide may be given to relieve symptoms in some patients with MCC. Radiation may be used to relieve pain from MCC that has metastasized to the brain or bones, and to reduce discomfort from skin problems associated with MCC (2). Additionally, meeting with a social worker, counselor, or member of the clergy can be helpful to those who want to talk about their feelings or discuss their concerns. A social worker can often suggest resources for help with recovery, emotional support, financial aid, transportation, or home care.

8. Are clinical trials (research studies) available? Where can people get more information about clinical trials?

Yes. The National Cancer Institute (NCI), a component of the National Institutes of Health, is sponsoring clinical trials that are designed to find new treatments and better ways to use current treatments. Before any new treatment can be recommended for general use, doctors conduct clinical trials to find out whether the treatment is safe for patients and effective against the disease. Participation in clinical trials may be a treatment option for patients with MCC.

People interested in taking part in a clinical trial should talk with their doctor. Information about clinical trials is available from the NCI's Cancer Information Service (CIS) (see below) at 1– 800– 4– CANCER and in the NCI booklet Taking Part in Cancer Treatment Research Studies , which can be found at http://www.cancer.gov/publications on the Internet. This booklet describes how research studies are carried out and explains their possible benefits and risks. Further information about clinical trials is available at http://www.cancer.gov/clinicaltrials on the NCI's Web site. The Web site offers detailed information about specific ongoing studies by linking to PDQ^®, the NCI's comprehensive cancer information database. The CIS also provides information from PDQ.

9. What is the prognosis for patients with Merkel cell carcinoma?

Prognosis describes the likely course and outcome of a disease—that is, the chance that a patient will recover or have a recurrence. The prognosis for MCC patients depends greatly on the stage of the disease at the time of diagnosis. If the tumor is small (less than 2 cm or about ¾ inch) and cancer cells have not spread to the lymph nodes, the 5-year survival rate is more than 90 percent. Patients with MCC that has spread to the lymph nodes have a 5-year survival rate of about 50 percent. Overall 5-year survival for patients diagnosed with MCC is 64 percent (7), but half of patients with advanced MCC will live only 9 months (2). The disease recurs in about 50 percent of patients (7). It is important to keep in mind, however, that these statistics are averages based on large numbers of patients. Statistics cannot be used to predict what will happen to a particular patient because each person's situation is unique.

Selected Reference

1. Wood GS, Bagheri M, Gharia M, et al. Nonmelanoma skin cancers: Basal cell and squamous cell carcinomas. In: Abeloff MD, Armitage JO, Niederhuber JE, Kastan MB, McKenna WG, editors. Clinical Oncology. 3rd ed. London: Churchill Livingstone, 2004.
   
   
2. Poulsen M. Merkel-cell carcinoma of the skin. Lancet Oncology 2004; 5(10):593– 599.
   
   
3. Camisa C, Weissmann A. Friedrich Sigmund Merkel. Part II. The cell. American Journal of Dermatopathology 1982; 4(6):527– 535.
   
   
4. Hodgson NC. Merkel cell carcinoma: Changing incidence trends. Journal of Surgical Oncology 2005; 89(1):1– 4.
   
   
5. Goessling W, McKee PH, Mayer RJ. Merkel cell carcinoma. Journal of Clinical Oncology 2002; 20(2):588– 598.
   
   
6. Miller RW, Rabkin CS. Merkel cell carcinoma and melanoma: Etiological similarities and differences. Cancer Epidemiology, Biomarkers & Prevention 1999; 8(2):153– 158.
   
   
7. Allen PJ, Bowne WB, Jaques DP, et al. Merkel cell carcinoma: Prognosis and treatment of patients from a single institution. Journal of Clinical Oncology 2005; 23(10): 2300– 2309.

# # #

• National Cancer Institute Fact Sheet 5.2, Computed Tomography (CT): Questions and Answers ¹
  (http://www.cancer.gov/cancertopics/factsheet/Detection/CT)
• National Cancer Institute Fact Sheet 5.32, Staging: Questions and Answers ²
  (http://www.cancer.gov/cancertopics/factsheet/Detection/staging)
• National Cancer Institute Fact Sheet 6.7, Cancer: Questions and Answers ³
  (http://www.cancer.gov/cancertopics/factsheet/Sites-Types/general)
• National Cancer Institute Fact Sheet 6.20, Metastatic Cancer: Questions and Answers ⁴
  (http://www.cancer.gov/cancertopics/factsheet/Sites-Types/metastatic)
• National Cancer Institute Fact Sheet 7.44, Sentinel Lymph Node Biopsy: Questions and Answers ⁵
  (http://www.cancer.gov/cancertopics/factsheet/therapy/sentinel-node-biopsy)
• Taking Part in Cancer Treatment Research Studies ⁶ (http://www.cancer.gov/clinicaltrials/Taking-Part-in-Cancer-Treatment-Research-Studies)
• What You Need To Know About™ Skin Cancer ⁷ (http://www.cancer.gov/cancertopics/wyntk/skin)

For more help, contact:

NCI's Cancer Information Service
Telephone (toll-free): 1–800–4–CANCER (1–800–422–6237)
TTY (toll-free): 1–800–332–8615
LiveHelp^® online chat: https://cissecure.nci.nih.gov/livehelp/welcome.asp

Glossary Terms

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

A quickly growing cancer.

A type of protein made by plasma cells (a type of white blood cell) in response to an antigen (foreign substance). Each antibody can bind to only one specific antigen. The purpose of this binding is to help destroy the antigen. Antibodies can work in several ways, depending on the nature of the antigen. Some antibodies destroy antigens directly. Others make it easier for white blood cells to destroy the antigen.

A poisonous chemical used to kill weeds and pests. Also used in cancer therapy.

A large group of single-cell microorganisms. Some cause infections and disease in animals and humans. The singular of bacteria is bacterium.

Not cancerous. Benign tumors may grow larger but do not spread to other parts of the body.

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 tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.

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.

The Cancer Information Service is the National Cancer Institute's link to the public, interpreting and explaining research findings in a clear and understandable manner, and providing personalized responses to specific questions about cancer. Access the CIS by calling 1-800-4-CANCER (1-800-422-6237), or by using the LiveHelp instant-messaging service at https://cissecure.nci.nih.gov/livehelp/welcome.asp. Also called CIS.

A drug that is used to treat symptoms of ovarian cancer that has come back after treatment with other anticancer drugs or to treat advanced ovarian cancer that has never been treated. It is also used together with other anticancer drugs to treat non-small cell lung cancer and is being studied in the treatment of other types of cancer. Carboplatin is a form of cisplatin that causes fewer side effects in patients. It attaches to DNA (the molecules inside cells that carry genetic information and pass it from one generation to the next) and may cause cancer cells to die. It is a type of platinum compound.

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.

Treatment with drugs that kill cancer cells.

A slow-growing type of leukemia (blood cancer) in which too many lymphoblasts (immature white blood cells) are found in the blood and bone marrow. Also called chronic lymphoblastic leukemia and CLL.

Ordained individuals who perform spiritual and/or religious functions.

A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease. Also called clinical study.

A series of detailed pictures of areas inside the body taken from different angles. The pictures are created by a computer linked to an x-ray machine. Also called CAT scan, computerized axial tomography scan, computerized tomography, and CT scan.

A sac or capsule in the body. It may be filled with fluid or other material.

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

Cells that look abnormal under a microscope but are not cancer.

Refers to tissue that makes and releases hormones that travel in the bloodstream and control the actions of other cells or organs. Some examples of endocrine tissues are the pituitary, thyroid, and adrenal glands.

A drug used to treat testicular and small cell lung cancers. It is also being studied in the treatment of several other types of cancer. Etoposide blocks certain enzymes needed for cell division and DNA repair, and it may kill cancer cells. It is a type of podophyllotoxin derivative and a type of topoisomerase inhibitor. Also called Toposar and Vepesid.

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.

Suppression of the body's immune system and its ability to fight infections and other diseases. Immunosuppression may be deliberately induced with drugs, as in preparation for bone marrow or other organ transplantation, to prevent rejection of the donor tissue. It may also result from certain diseases such as AIDS or lymphoma or from anticancer drugs.

The number of new cases of a disease diagnosed each year.

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.

Use of a syringe and needle to push fluids or drugs into the body; often called a "shot."

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.

The tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases. This system includes the bone marrow, spleen, thymus, lymph nodes, and lymphatic vessels (a network of thin tubes that carry lymph and white blood cells). Lymphatic vessels branch, like blood vessels, into all the tissues of the body.

The edge or border of the tissue removed in cancer surgery. The margin is described as negative or clean when the pathologist finds no cancer cells at the edge of the tissue, suggesting that all of the cancer has been removed. The margin is described as positive or involved when the pathologist finds cancer cells at the edge of the tissue, suggesting that all of the cancer has not been removed.

A form of cancer that begins in melanocytes (cells that make the pigment melanin). It may begin in a mole (skin melanoma), but can also begin in other pigmented tissues, such as in the eye or in the intestines.

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 surgical procedure used to treat skin cancer. Individual layers of cancerous tissue are removed and examined under a microscope one at a time until all cancerous tissue has been removed. Also called Mohs micrographic surgery.

A benign (noncancerous) growth on the skin that is formed by a cluster of melanocytes (cells that make a substance called melanin, which gives color to skin and eyes). A mole is usually dark and may be raised from the skin. Also called nevus.

The National Cancer Institute, part of the National Institutes of Health of the United States Department of Health and Human Services, is the Federal Government's principal agency for cancer research. The National Cancer Institute conducts, coordinates, and funds cancer research, training, health information dissemination, and other programs with respect to the cause, diagnosis, prevention, and treatment of cancer. Access the National Cancer Institute Web site at http://www.cancer.gov. Also called NCI.

A federal agency in the U.S. that conducts biomedical research in its own laboratories; supports the research of non-Federal scientists in universities, medical schools, hospitals, and research institutions throughout the country and abroad; helps in the training of research investigators; and fosters communication of medical information. Access the National Institutes of Health Web site at http://www.nih.gov. Also called NIH.

The organized network of nerve tissue in the body. It includes the central nervous system (the brain and spinal cord), the peripheral nervous system (nerves that extend from the spinal cord to the rest of the body), and other nerve tissue.

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.

Skin cancer that forms in basal cells or squamous cells but not in melanocytes (pigment-producing cells of the skin).

A type of radionuclide scan used to find carcinoid and other types of tumors. Radioactive octreotide, a drug similar to somatostatin, is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to tumor cells that have receptors for somatostatin. A radiation-measuring device detects the radioactive octreotide, and makes pictures showing where the tumor cells are in the body. Also called somatostatin receptor scintigraphy and SRS.

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.

PDQ is an online database developed and maintained by the National Cancer Institute. Designed to make the most current, credible, and accurate cancer information available to health professionals and the public, PDQ contains peer-reviewed summaries on cancer treatment, screening, prevention, genetics, complementary and alternative medicine, and supportive care; a registry of cancer clinical trials from around the world; and directories of physicians, professionals who provide genetics services, and organizations that provide cancer care. Most of this information, and more specific information about PDQ, can be found on the NCI's Web site at http://www.cancer.gov/cancertopics/pdq. Also called Physician Data Query.

A procedure in which a small amount of radioactive glucose (sugar) is injected into a vein, and a scanner is used to make detailed, computerized pictures of areas inside the body where the glucose is used. Because cancer cells often use more glucose than normal cells, the pictures can be used to find cancer cells in the body. Also called positron emission tomography scan.

The original tumor.

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.

The overall enjoyment of life. Many clinical trials assess the effects of cancer and its treatment on the quality of life. These studies measure aspects of an individual’s sense of well-being and ability to carry out various activities.

The use of high-energy radiation from x-rays, gamma rays, neutrons, protons, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy). Systemic radiation therapy uses a radioactive substance, such as a radiolabeled monoclonal antibody, that travels in the blood to tissues throughout the body. Also called irradiation and radiotherapy.

A drug containing a radioactive substance that is used in the diagnosis and treatment of cancer and in pain management of bone metastases. Also called radiopharmaceutical.

Cancer that has recurred (come back), usually after a period of time during which the cancer could not be detected. The cancer may come back to the same place as the original (primary) tumor or to another place in the body. Also called recurrent cancer.

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.

A picture of structures inside the body. Scans often used in diagnosing, staging, and monitoring disease include liver scans, bone scans, and computed tomography (CT) or computerized axial tomography (CAT) scans and magnetic resonance imaging (MRI) scans. In liver scanning and bone scanning, radioactive substances that are injected into the bloodstream collect in these organs. A scanner that detects the radiation is used to create pictures. In CT scanning, an x-ray machine linked to a computer is used to produce detailed pictures of organs inside the body. MRI scans use a large magnet connected to a computer to create pictures of areas inside the body.

In medicine, an instrument that takes pictures of the inside of the body.

The first lymph node to which cancer is likely to spread from the primary tumor. When cancer spreads, the cancer cells may appear first in the sentinel node before spreading to other lymph nodes.

Removal and examination of the sentinel node(s) (the first lymph node(s) to which cancer cells are likely to spread from a primary tumor). To identify the sentinel lymph node(s), the surgeon injects a radioactive substance, blue dye, or both near the tumor. The surgeon then uses a scanner to find the sentinel lymph node(s) containing the radioactive substance or looks for the lymph node(s) stained with dye. The surgeon then removes the sentinel node(s) to check for the presence of cancer cells.

A problem that occurs when treatment affects healthy tissues or organs. Some common side effects of cancer treatment are fatigue, pain, nausea, vomiting, decreased blood cell counts, hair loss, and mouth sores.

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.

An aggressive (fast-growing) cancer that forms in tissues of the lung and can spread to other parts of the body. The cancer cells look small and oval-shaped when looked at under a microscope.

A professional trained to talk with people and their families about emotional or physical needs, and to find them support services.

A type of radionuclide scan used to find carcinoid and other types of tumors. Radioactive octreotide, a drug similar to somatostatin, is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to tumor cells that have receptors for somatostatin. A radiation-measuring device detects the radioactive octreotide, and makes pictures showing where the tumor cells are in the body. Also called octreotide scan and SRS.

Having to do with deep, often religious, feelings and beliefs, including a person’s sense of peace, purpose, connection to others, and beliefs about the meaning of life.

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.

Care given to improve the quality of life of patients who have a serious or life-threatening disease. The goal of supportive care is to prevent or treat as early as possible the symptoms of a disease, side effects caused by treatment of a disease, and psychological, social, and spiritual problems related to a disease or its treatment. Also called comfort care, palliative care, and symptom management.

A doctor who removes or repairs a part of the body by operating on the patient.

A procedure to remove or repair a part of the body or to find out whether disease is present. An operation.

The percentage of people in a study or treatment group who are alive for a certain period of time after they were diagnosed with or treated for a disease, such as cancer. The survival rate is often stated as a five-year survival rate, which is the percentage of people in a study or treatment group who are alive five years after diagnosis or treatment. Also called overall survival rate.

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.

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.

Invisible rays that are part of the energy that comes from the sun. Ultraviolet radiation also comes from sun lamps and tanning beds. It can damage the skin and cause melanoma and other types of skin cancer. Ultraviolet radiation that reaches the Earth's surface is made up of two types of rays, called UVA and UVB rays. UVB rays are more likely than UVA rays to cause sunburn, but UVA rays pass deeper into the skin. Scientists have long thought that UVB radiation can cause melanoma and other types of skin cancer. They now think that UVA radiation also may add to skin damage that can lead to skin cancer and cause premature aging. For this reason, skin specialists recommend that people use sunscreens that reflect, absorb, or scatter both kinds of ultraviolet radiation. Also called UV radiation.

A term used to describe cells or tissues that do not have specialized ("mature") structures or functions. Undifferentiated cancer cells often grow and spread quickly.

A type of high-energy radiation. In low doses, x-rays are used to diagnose diseases by making pictures of the inside of the body. In high doses, x-rays are used to treat cancer.