Medical Glossary M

M proteins: Antibodies or parts of antibodies found in unusually large amounts in the blood or urine of multiple myeloma patients.

Maintenance therapy: Chemotherapy that is given to leukemia patients in remission to prevent a relapse.

Mastectomy (mas-TEK-to-mee): Surgery to remove the breast (or as much of the breast as possible).

Mediastinoscopy (MEE-dee-a-stin-AHS-ko-pee): A procedure in which the doctor inserts a tube into the chest to view the organs in the mediastinum. The tube is inserted through an incision above the breastbone.

Mediastinotomy (MEE-dee-a-stin-AH-toe-mee): A procedure in which the doctor inserts a tube into the chest to view the organs in the mediastinum. The tube is inserted through an incision next to the breastbone.

Mediastinum (mee-dee-a-STY-num): The area between the lungs. The organs in this area include the heart and its large veins and arteries, the trachea, the esophagus, the bronchi, and lymph nodes.

Medulloblastoma (MED-yoo-lo-blas-TOE-ma): A type of brain tumor that recent research suggests develops from primitive (developing) nerve cells that normally do not remain in the body after birth. Medulloblastomas are sometimes called primitive neuroectodermal tumors. They are almost always found in children or young adults.

Melanin (MEL-a-nin): A skin pigment (substance that gives the skin its color). Dark-skinned people have more melanin than light-skinned people.

Melanocytes (mel-AN-o-sites): Cells in the skin that produce and contain the pigment called melanin.

Melanoma (MEL-an-O-ma): Melanoma is a very serious form of skin cancer. It begins in melanocytes— cells that make the skin pigment called melanin. Although melanoma accounts for only about 4% of all skin cancer cases, it causes most skin cancer-related deaths. The good news is that melanoma is often curable if it is detected and treated in its early stages. In men, melanoma is found most often on the area between the shoulders and hips or on the head and neck. In women, melanoma often develops on the lower legs. It may also appear under the fingernails or toenails or on the palms or soles. The chance of developing melanoma increases with age, but it affects all age groups and is one of the most common cancers in young adults. See Skin Cancer.

Membrane: A very thin layer of tissue that covers a surface.

Meninges (meh-NIN-jeez): The three membranes that cover the brain and spinal cord.

Meningioma (meh-nin-jee-O-ma): A type of brain tumor that develops in the meninges. Because these tumors grow very slowly, the brain may be able to adjust to their presence; meningiomas often grow quite large before they cause symptoms.

Menopause (MEN-o-pawz): The time of a woman's life when menstrual periods permanently stop. Also called "change of life."

Menstrual cycle (MEN-stroo-al): The hormone changes that lead up to a woman's having a period. For most women, one cycle takes 28 days.

Mesothelioma: Malignant mesothelioma, a rare form of cancer, is a disease in which cancer (malignant) cells are found in the sac lining the chest (the pleura) or abdomen (the peritoneum). Most people with malignant mesothelioma have worked on jobs where they breathed asbestos.

Microcalcifications (MY-krow-kal-si-fi-KA-shunz): Tiny deposits of calcium in the breast that cannot be felt but can be detected on a mammogram. A cluster of these very small specks of calcium may indicate that cancer is present.

Mole: An area on the skin (usually dark in color) that contains a cluster of melanocytes.

Monoclonal antibodies (MON-o-KLO-nul AN-ti-BOD-eez): Substances that can locate and bind to cancer cells wherever they are in the body. They can be used alone, or they can be used to deliver drugs, toxins, or radioactive material directly to tumor cells.

Monocyte: A type of white blood cell.

Morphology: The science of the form and structure of organisms (plants, animals, and other forms of life).

MRI (magnetic resonance imaging): A procedure in which a magnet linked to a computer is used to create detailed pictures of areas inside the body.

Mucus: A thick fluid produced by the lining of some organs of the body.

Multiple myeloma (mye-eh-LO-ma): Cancer that affects plasma cells. The disease causes the growth of tumors in many bones, which can lead to bone pain and fractures. In addition, the disease often causes kidney problems and lowered resistance to infection.

Mutations: Changes in the way cells function or develop, caused by an inherited genetic defect or an environmental exposure. Such changes may lead to cancer.

Mycosis fungoides (my-KO-sis fun-GOY-deez): A type of non-Hodgkin's lymphoma that first appears on the skin. Also called cutaneous T-cell lymphoma.

Myelin (MYE-eh-lin): The fatty substance that covers and protects nerves.

Myelodysplastic syndrome (MYE-eh-lo-dis-PLAS-tik SIN-drome): Myelodysplastic syndromes, also called pre-leukemia or "smoldering" leukemia, are diseases in which the bone marrow does not function normally and not enough normal blood cells are made. See Preleukemia

Myelogenous (mye-eh-LAH-jen-us): Referring to myelocytes, a type of white blood cell. Also called myeloid.

Myelogram (MYE-eh-lo-gram): An x-ray of the spinal cord and the bones of the spine.

Myeloid (MYE-eh-loyd): Referring to myelocytes, a type of white blood cell. Also called myelogenous.

Myometrium (my-o-MEE-tree-um): The muscular outer layer of the uterus.