Definitions of medical terms relevant to Merkel cell carcinoma (MCC)

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adjuvant therapy
Refers to additional treatment, after all detectable disease has been removed (usually by surgery), but where there remains a risk of relapse.  If known disease is left behind following surgery, then further treatment is not technically "adjuvant."


basal cell carcinoma
Skin cancer that arises from basal cells, a cell type found in the innermost layer of the epidermis.  Compared to other skin cancers, basal cell carcinoma is rarely lethal.  Less than 1 in 50,000 patients with basal cell carcinoma will die from this disease.

Not cancerous.  Unlike malignant tumors, benign tumors do not spread widely throughout the body, aggressively invade local structures or result in death.

The removal of cells or tissue in order to determine the presence, characteristics, or extent of a disease by a pathologist usually using microscopic analysis.

bone scan
A technique used to create images of bones to aid in evaluating the type or extent of disease.  It can be used to identify cancer in bones.  A radioactive dye is injected into the veins and collects in areas of bone that are being broken down or reformed as can occur when cancer invades bone, or when bone is healing after a break.

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A term used to describe diseases in which abnormal cells continually divide without normal regulation.  Cancerous cells may invade surrounding tissues and may spread to other regions of the body via blood and the lymphatic system.

A "chemotherapy" drug in the class of DNA alkylating agents that is used to treat some types of cancer.  It is closely related to cisplatin but has fewer side effects.  Carboplatin link.

Cancer that originates in the skin or in the tissues lining the gut and ducts.

CAT scan
A series of detailed 3-dimensional 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 computerized axial tomography scan, computed tomography scan, CT scan, and computerized tomography.  Contrast dye may be injected or taken orally to aid in accurately interpreting where in the body lesions occur.

Treatment with drugs to kill cancer cells or to render them less active.  May be given intravenously or orally depending on the drug and situation.

chronic lymphocytic leukemia (CLL)
A slow-growing type of leukemia (white blood cell cancer) associated with immune suppression.  Patients with CLL have a markedly increased risk and severity of Merkel cell carcinoma.

An anticancer drug commonly used in combination with etoposide for neuroendocrine cancers such as small cell lung cancer and Merkel cell carcinomaCisplatin link.

CT scan
See CAT scan.

cytokeratin 20 (CK20)
Protein expressed by normal and malignant Merkel cells often used to make a diagnosis of Merkel cell carcinoma.

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The deeper layer of the two main tissue layers that make-up the skin.  The dermis is below the epidermisMerkel cells are normally in the epidermis.  In MCC, they grow and invade into the dermis and deeper structures and vessels.

A doctor who has special training in the diagnosis and treatment of skin diseases, including cancers of the skin.

draining lymph node
The particular lymph node(s) to which the lymph fluid from an area of tissue flows.


The outermost layer of the two main layers that make-up the skin.  Merkel cells normally exist in the basal layer of the epidermis, usually about 0.1 mm from skin's surface.  View epidermis picture.

An anticancer drug used as a form of chemotherapy.  It is often given intravenously or orally in combination with other drugs.  Etoposide combined with carboplatin (or cisplatin) is a common therapy for Merkel cell carcinoma in its advanced stages.

The removal of tissue of interest by surgery.

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An area of abnormal tissue that may be either benign or malignant.

Affecting only the site of origin, without evidence of spreading.  Compare to systemic.

Includes the area of the primary tumor and first draining lymph nodes but not beyond.

lymph node
A rounded mass of lymphatic tissue that is usually surrounded by connective tissue and about the size of a green pea.  Lymph nodes filter lymphatic fluid, also know as lymph, which is fluid that drains from the tissues of the body and contains immune cells.  Cancer cells often travel through lymph vessels and lodge and grow in lymph nodes, sometimes causing the nodes to markedly increase in size.

lymphatic system
The tissues and organs that produce and carry white blood cells that fight infection and disease.  This system includes lymph nodes, lymphatic vessels, bone marrow, the spleen and thymus.

lymphatic vessels
Thin tubes that carry lymph (also called lymphatic fluid) including white blood cells through the lymphatic system to lymph nodes and eventually back into the bloodstream.  Lymphatic vessels originate in the tissues of the body like blood vessels.

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Having the ability to grow without normal regulation, to invade local tissues aggressively and/or spread throughout the body.

The edge or perimeter of the tissue removed in cancer surgery.  The margin is described as "clear" or "negative" when the pathologist sees no sign of cancer cells under the microscope, suggesting that all of the cancer has been removed.  The margin is described as "positive" or "involved" when the pathologist finds cancer cells in the edge of the tissue.  This suggests that not all of the cancer has been removed.  Certain cancers such as Merkel cell carcinoma can have negative microscopic margins despite residual cancer cells being left behind because MCC often "skips" via local lymphatics to adjacent areas and does not grow a single continuous mass.

medical oncologist
A doctor who specializes in the diagnosis and treatment of cancer patients especially using chemotherapy.

A form of skin cancer that begins in melanocytes (the skin cells that produce the pigment melanin).  Melanoma affects about 42,000 Americans per year and has about a 15% mortality.

Merkel cell
Merkel cells are found in the lower part of the epidermis.  Although the exact function of Merkel cells is unknown, they are thought to be touch receptors.  Also known as neuroendocrine cells, they have machinery similar to nerve cells and to hormone-secreting (endocrine) cells.

Merkel cell carcinoma (MCC)
A skin cancer that is believed to arise from Merkel cells in the epidermis.  MCC was first described in 1972 and only in the 1990s was the CK20 antibody developed to make it easily identified by pathologists.  Many doctors and patients are not aware of this cancer because of its recent description and relative rarity (1500 cases/year in the US--roughly 30 times less common than melanoma).  Approximately 33% of MCC patients will die of this disease, making it far more serious than most other types of skin cancer.

Having to do with the spread of cancer from a primary site of origin to distant areas beyond the draining lymph nodes.

Mohs surgery
Also called "Mohs micrographic surgery".  A surgical procedure used to treat some skin cancers.  Circumferential (like an onion) tissue layers are removed and examined under a microscope one at a time until all cancerous tissues appear to have been removed.  While it is occasionally an appropriate therapy for Merkel cell carcinoma, Mohs surgery is an optimal therapy for tumors such as basal cell carcinoma on locations for which minimizing surgical margins is important (face, etc.).  Mohs surgery usually cannot be performed at the same time as a sentinel lymph node biopsy, which may be very important for MCC management.

Magnetic resonance imaging. A procedure in which radio waves and a powerful magnet linked to a computer are used to create detailed pictures of areas inside the body. These pictures can show the difference between normal and diseased tissue.  MRI does not involve radiation and is especially useful for imaging the brain, the spine, the soft tissue of joints, and the inside of bones.  CT or PET CT, rather than MRI, are the typical choices for evaluating a patient for evidence of metastatic cancer.

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Neuroendocrine refers to the type of cells that make up Merkel cell carcinoma. "Neuro-" means that these cells have some sensory function related to the nervous system, while "endocrine-" refers to hormonal types of cells.  Merkel cells have both such features.

nodal presentation
Describes when cancer has spread to the lymph nodes usually with no evidence of a primary lesion.  About 10-15% of MCC patients present with disease that is only found in the lymph nodes.  It is likely that in most such cases, a primary lesion occurred on nearby skin and was destroyed by the immune system after it released some cells that spread to the draining lymph nodes.


A doctor who specializes in treating cancer.  Three main types of oncologists exist: radiation oncologist, medical oncologist, and surgical oncologist.

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Relieving pain or decreasing the severity of a disease.  Palliative therapy is usually contrasted with curative therapy (given with intent to cure the patient of cancer).

A doctor who specializes in identifying diseases by examining cells and tissues under a microscope.

PET CT scan
"Positron emission tomography computed tomography" scan.  A procedure in which a small amount of radioactive glucose (sugar) is injected into the blood through a vein and a scanner is used to create computerized pictures that indicate the areas of the body where the glucose is used.  Cancer cells tend to use more glucose than normal cells, therefore, these images help find cancer cells in the body.  A CT scan is usually done at the same time to aid in determining exactly where in the body the abnormal glucose uptake is occuring.

primary lesion
The abnormal tissue that appeared first.  The majority of Merkel cell carcinoma primary lesions occur in sun-exposed areas.  In some cases of MCC (approximately 11%) the patient has no primary lesion and instead has a nodal presentation (disease in a lymph node only).  In these cases the primary lesion likely was destroyed by the immune system.

primary site
The area of the body where the abnormal tissue first appeared.

Relates to the outcome, course of a disease, or chance of cure.

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radiation oncologist
A doctor who specializes in using radiation to treat cancer.  X-rays ("photons") are used to penetrate more deeply and "electron" beam therapy is used to target more superficial cancer sites.

radiation therapy
The use of radiation to kill cancer cells and shrink tumors.  Merkel cell carcinoma is a highly radiation sensitive cancer in most cases.  Radiation may come from a treatment machine (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy) or "seeds."  Some common acute (during and for a few weeks after treatment) side effects include burns like sunburn, ulcers, and fatigue.  Some common chronic (beginning months to years later) side effects include thin skin, scar-like changes, decreased mobility of joints within the field, and swelling of the arm or leg if lymph nodes are treated in the axilla or groin.  More than 10 years later there is an increased risk of skin cancer.

A disappearance of or decrease in the signs and symptoms of cancer.  In complete remission, all signs and symptoms of cancer have disappeared; however, cancer may still be present in the body.  In partial remission, only some signs and symptoms have gone away.


sentinel lymph node biopsy
Removal and examination of the "sentinel" lymph node(s).  Sentinel nodes are the first lymph nodes to which cancer cells spread from a primary lesion.  To identify the sentinel lymph node(s), a radioactive substance and/or dye is injected near the primary lesion.  The surgeon uses a Geiger counter to find the lymph node(s) containing the radioactive substance or looks for the lymph node(s) stained by the dye.  The surgeon then removes the sentinel lymph node(s) and sends them to a pathologist to check for the presence of cancer.

small cell lung carcinoma
A cancer that grows in lung tissue and may spread to other areas of the body.  This cancer has abnormal "neuroendocrine" cells that look like the cancer cells in Merkel cell carcinoma under the microscope.  Importantly, optimal management for MCC is often not the same as that for small cell lung carcinoma (SCLC).

squamous cell carcinoma
Squamous cell carcinoma is a cancer that begins in squamous cells, which are thin, flat cells.  Squamous cells are located in the middle layers of the epidermis, the lining of portions of the respiratory and digestive tracts, and the lining of some organs.  Squamous cell carcinoma affects about 100,000 Americans and has a mortality of roughly 2%.

Physicians determine the stage of cancer by performing physical exams and tests.  Stages describe the extent of cancer within the body, especially whether the disease has spread (metastasized) from the primary site to other parts of the body.  Knowing the stage of the disease is important in order to plan the best treatment to help predict survival.  Currently, for Merkel cell carcinoma, there are four distinct (conflicting) staging systems in use, leading to much confusion.  In 2008, the American Joint Committee on Cancer will publish a single staging system for MCC based on the outcome of thousands of patients.

surgical oncologist
A doctor who specializes in performing surgeries related to cancer.

Affecting the entire body.  Compare to local.

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T lymphocytes
Cells belonging to a group of white blood cells that play a central role in cell-mediated immunity.  These cells seem to be very important in preventing and fighting Merkel cell carcinoma.  Patients with defects in T lymphocyte function include HIV, kidney/heart/liver transplant recipients and chronic lymphocytic leukemia patients.  All of these groups have a 10-30 fold increased risk of MCC, and a lower chance of beating MCC once it has occured.




wide surgical excision
An excision taken with wide margins, generally approximately 1cm or greater in an attempt to surgically remove a cancer.


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



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