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Glossary - M

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  • Magnetic resonance imaging

    (mag-NEH-tik REH-zuh-nunts IH-muh-jing)

    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 makes better images of organs and soft tissue than other scanning techniques, such as computed tomography (CT) or x-ray. MRI is especially useful for imaging the brain, the spine, the soft tissue of joints, and the inside of bones. Also called magnetic resonance imaging, NMRI, and nuclear magnetic resonance imaging.

  • Malignant


    Tending to grow and spread in a rapid and uncontrolled way.

  • Malignant tumor

    A mass of cancer cells that may invade surrounding tissues or spread (metastasize) to distant areas of your body.

  • Malnutrition


    A condition caused by not getting enough calories or the right amount of key nutrients, such as vitamins and minerals, that are needed for health. Malnutrition may occur when there is a lack of nutrients in the diet or when the body cannot absorb nutrients from food. Cancer and cancer treatment may cause malnutrition.

  • Manual healing

    (MAN-yoo-ul HEE-ling)

    A type of therapy in which the therapist moves or manipulates one or more parts of the patient’s body. It may be used to treat pain, stress, anxiety, and depression, and for general well-being. Examples include chiropractic treatments, physical therapy, and massage therapy. Also called manipulative and body-based practice and physical touch methods.

  • Marker


    A diagnostic indication that disease may develop.

  • Mass


    In medicine, a lump in the body. It may be caused by the abnormal growth of cells, a cyst, hormonal changes, or an immune reaction. A mass may be benign (not cancer) or malignant (cancer).

  • Mast cell

    (mast sel)

    A type of white blood cell.

  • Mean survival

    (meen ser-VY-vul)

    The average length of time from either the date of diagnosis or the start of treatment for a disease, such as cancer, that patients diagnosed with the disease are still alive. In a clinical trial, measuring mean survival is one way to see how well a new treatment works.

  • Measurable disease

    (MEH-zur-uh-bul dih-ZEEZ)

    A tumor that can be accurately measured in size. This information can be used to judge response to treatment.

  • Median survival

    (MEE-dee-un ser-VY-vul)

    The length of time from either the date of diagnosis or the start of treatment for a disease, such as cancer, that half of the patients in a group of patients diagnosed with the disease are still alive. In a clinical trial, measuring the median survival is one way to see how well a new treatment works. Also called median overall survival.

  • Mediastinoscope


    A thin, tube-like instrument used to examine the tissues and lymph nodes in the area between the lungs. These tissues include the heart and its large blood vessels, trachea, esophagus, and bronchi. The mediastinoscope has a light and a lens for viewing and may also have a tool to remove tissue. It is inserted into the chest through a cut above the breastbone.

  • Mediastinum


    The area between the lungs. The organs in this area include the heart and its large blood vessels, the trachea, the esophagus, the thymus, and lymph nodes but not the lungs.

  • Medical history

    MEH-dih-kul HIH-stuh-ree

    A record of information about a person’s health. A personal medical history may include information about allergies, illnesses, surgeries, immunizations, and results of physical exams and tests. It may also include information about medicines taken and health habits, such as diet and exercise. A family medical history includes health information about a person's close family members (parents, grandparents, children, brothers, and sisters). This includes their current and past illnesses. A family medical history may show a pattern of certain diseases in a family.

  • Medical oncologist

    (MEH-dih-kul on-KAH-loh-jist)

    A doctor who has special training in diagnosing and treating cancer using chemotherapy, hormonal therapy, biological therapy, and targeted therapy. A medical oncologist often is the main health care provider for someone who has cancer. A medical oncologist also gives supportive care and may coordinate treatment given by other specialists.

  • Medication


    A legal drug that is used to prevent, treat, or relieve symptoms of a disease or abnormal condition.

  • Medicine


    A substance used in treating disease.

  • Medulloblastoma


    A malignant brain tumor that begins in the lower part of the brain and that can spread to the spine or to other parts of the body. Medulloblastomas are a type of primitive neuroectodermal tumor (PNET).

  • Melanocytes


    A cell in the skin and eyes that produces and contains the pigment called melanin.

  • Melanoma


    A cancerous (malignant) tumor that begins in the cells that produce the skin coloring (melanocytes). Melanoma is almost always curable in its early stages. However, it is likely to spread, and once it has spread to other parts of the body the chances for a cure are much less.

  • MEN syndrome

    ... SIN-drome

    An inherited condition that may result in the development of cancers of the endocrine system. There are several types of MEN syndrome, and patients with each type may develop different types of cancer. The altered genes that cause each type can be detected with a blood test. Also called multiple endocrine neoplasia syndrome.

  • Meningeal leukemia

    (meh-NIN-jee-ul loo-KEE-mee-uh)

    When the meninges, the membranes which cover the brain and the spinal cord, become invaded by leukemic cells.

  • Meningitis


    An infection of the membranes and fluid around the brain and spinal cord.

  • Menopause


    The time of life when a woman’s ovaries stop producing hormones and menstrual periods stop. Natural menopause usually occurs around age 50. A woman is said to be in menopause when she hasn’t had a period for 12 months in a row. Symptoms of menopause include hot flashes, mood swings, night sweats, vaginal dryness, trouble concentrating, and infertility.

  • Menstrual periods

    (MEN-stroo-ul PEER-ee-uds)

    The periodic discharge of blood and tissue from the uterus. From puberty until menopause, menstruation occurs about every 28 days, but does not occur during pregnancy.

  • Menstruation


    Periodic discharge of blood and tissue from the uterus. From puberty until menopause, menstruation occurs about every 28 days when a woman is not pregnant.

  • Mercaptopurine


    A drug used with other drugs to treat acute lymphoblastic leukemia. It is also being studied in the treatment of other types of cancer. Mercaptopurine stops cells from making DNA and may kill cancer cells. It is a type of antimetabolite. Also called Purinethol and Purixan.

  • Metabolic syndrome

    MEH-tuh-BAH-lik SIN-drome

    A condition marked by extra fat around the abdomen, high levels of blood glucose (sugar) when not eating, high levels of triglycerides (a type of fat) in the blood, low levels of high-density lipoproteins (a type of protein that carries fats) in the blood, and high blood pressure. People with metabolic syndrome are at increased risk of diabetes mellitus and diseases of the heart and blood vessels. Also called metabolic syndrome X.

  • Metabolism


    A general term for the many chemical processes that are necessary within the body to sustain life.

  • Metastasis

    The spread of cancer cells to distant areas of the body by way of the lymph system or bloodstream.

  • Metastasize


    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.

  • Metastatic


    Having to do with metastasis, which is the spread of cancer from the primary site (place where it started) to other places in the body.

  • Methodology


    In medicine, the rules and procedures for doing research and evaluating results.

  • Microorganism


    A general name for any small living organism, such as bacteria, viruses, and fungi.

  • Mitigate


    To make milder or less painful.

  • Mitochondria


    Small structures in a cell that are found in the cytoplasm (fluid that surrounds the cell nucleus). Mitochondria make most of the energy for the cell and have their own genetic material that is different from the genetic material found in the nucleus. Many diseases are caused by mutations (changes) in the DNA of mitochondria. Mitochondria are cell organelles.

  • Mitotane


    An anticancer drug used in treating adrenocortical cancer and ACTH-producing pituitary tumors (Cushing disease).

  • Mixed lymphocyte culture assay

    A technique to determine compatibility between individuals. Differences in HL-A antigens between two individuals will cause an immune reaction between their lymphocytes mixed in culture. This reactivity can be measured in the MLC assay. Compatible individuals have negative MLC's.

  • Modality


    A method of treatment. For example, surgery and chemotherapy are treatment modalities.

  • Moderate sedation

    (MAH-deh-rut seh-DAY-shun)

    A level of sedation in which a person is asleep but wakes when spoken to or touched. Moderate sedation is caused by special drugs and is used to help relieve anxiety during certain medical or surgical procedures. Drugs that relieve pain may be given at the same time. Also called conscious sedation.

  • Monitor


    A machine that continually records your heart activity.

  • Monoclonal antibodies

    Antibodies made in the laboratory and designed to target specific substances called antigens. Monoclonal antibodies which have been attached to chemotherapy drugs or radioactive substances are being studied to see if they can seek out antigens unique to cancer cells and deliver these treatments directly to the cancer, thus killing the cancer cells without harming healthy tissue. Monoclonal antibodies are also used in other ways, for example, to help find and classify cancer cells.

  • Monocyte


    A type of young white blood cell.

  • mTOR inhibitor

    (… in-HIH-bih-ter)

    A substance that blocks a protein called mTOR, which helps control cell division. Blocking mTOR’s action may keep cancer cells from growing and prevent the growth of new blood vessels that tumors need to grow. Some mTOR inhibitors are used to treat cancer.

  • Mucosa


    The moist, inner lining of some organs and body cavities (such as the nose, mouth, lungs, and stomach). Glands in the mucosa make mucus (a thick, slippery fluid). Also called mucous membrane.

  • Mucositis


    Inflammation of the mucous membrane, e.g. Inside the mouth.

  • Mucous membrane

    (MYOO-kus MEM-brayn)

    A lining of the internal surface of the body which produces mucous.

  • Multidrug resistance

    (MUL-tee-... reh-ZIH-stunts)

    Adaptation of tumor cells to anticancer drugs in ways that make the drugs less effective.

  • Multigene test

    (MUL-tee-jeen ...)

    A laboratory test in which many genes are studied in a sample of tissue. Multigene tests may help find mutations (changes) in certain genes that may increase a person’s risk of a disease such as cancer. They may also look at the activity of certain genes in a sample of tissue. Multigene tests may be used to help plan treatment or make a prognosis, including helping to predict whether cancer will spread to other parts of the body or come back. Also called multiple-gene panel test and multiple-gene test.

  • Musculoskeletal


    Having to do with muscles, bones, tendons, ligaments, joints, and cartilage.

  • Mutate


    To change the genetic material of a cell. The changes (mutations) can be harmful, beneficial, or have no effect.

  • Mutation


    Any change in the DNA sequence of a cell. Mutations may be caused by mistakes during cell division, or they may be caused by exposure to DNA-damaging agents in the environment. Mutations can be harmful, beneficial, or have no effect. If they occur in cells that make eggs or sperm, they can be inherited; if mutations occur in other types of cells, they are not inherited. Certain mutations may lead to cancer or other diseases.

  • MYCN gene

    (... jeen)

    MYCN is important for cell growth. Having more than 10 copies of the gene is called MYCN amplification. Neuroblastoma with MYCN amplification is more likely to spread in the body and less likely to respond to treatment.

  • Myelin


    The fatty substance that covers and protects nerves.

  • Myelosuppression


    A reduction in platelets, red cells and white cells, as a result of decreased bone marrow activity. Platelets are the blood cells that prevent or stop bleeding. White blood cells help prevent infections.