Macroglobulin: A plasma globulin with high molecular weight such as IgM secreted in excess in small cell lymphoma. Macrophages: Many forms of mononuclear phagocytes found in tissues. They perform many functions including killing of ingested microorganisms, digestion and presentation of antigens to T and B-lymphocytes and secretion of a large number of diverse products. Magnetic resonance imaging: Powerful magnets and computers are used to produce a three dimensional image of internal tissues. This is a noninvasive technique. Malignant tumor: Cancerous cells that break away from the tissue of origin and eventually produce secondary tumor in other parts of the body. Mammogram: Low radiation X-ray to visualize the inner structure of mammary gland. X-ray cannot pass through the solid tumor so it produces white image on the film. Mannose: A hexose (6-carbon compound) or fermentable monosaccharide and isomer of glucose from manna, the ash fraxinus ornus and related plants. Mast cell: Connective tissue cell whose specific physiologic function remains unknown; capable of producing cytoplasmic granules that contain histamine, heparin. Mastocytosis: A condition characterized by infiltration of mast cells into the tissues of the body. Mast cells are connective tissue cells which release chemicals including histamine that are very irritating and cause itching, swelling, and fluid leakage from cells. There are several different clinical forms of mastocytosis. MDM2: The mouse double minute 2 oncogene product, which binds to p53, blocking its function. MDM2 is amplified or overexpressed in many human cancers. High MDM2 levels is associated with poor prognosis. MDR1: Gene for the protein that elicits multidrug resistance. Melanocytes: Cells that produce a pigment called melanin. Melanocytes are normally present in the skin. They are also present in the eye and the nervous system. Amount of melanin present in the melanocytes gives the varying degrees of skin coloration. Memory T cells: When activated by specific antigens, T cells proliferate and differentiate to memory T cells that remember the antigen, which activated it. In the future if the same antigen is encountered the memory T cells will recognize it. Menarche: The beginning of the menstrual cycle. Mendelian's rule: The law of inheritance of single-gene traits that form the basis of the science of genetics, first described by Gregor Mendel in 1865. From experimental crosses of pea plants differing in one or more characteristics determined by single genes, and counting the types of progeny in successive generations, Mendel derived two laws now usually expressed as the law of segregation (the members of a pair of allelic genes segregate from one another and pass to different gametes) and the law of independent assortment (genes that are not allele are distributed to the gametes independently of one another). Meningiomas: Hard, slow growing, usually vascular tumors that grow mainly along the meningeal (membranes that envelop the brain and the spinal cord) vessels invading the brain and skull. Mesangial cells: Cells of the thin membrane, which helps to support in capillary loops in renal glomerulus. Mesenchyma: The meshwork of embryonic connective tissue in the mesoderm from which are formed the connective tissues of the body, and also the blood vessels and lymphatic vessels. Mesenchymal cell: Cells of the mesenchyma, the meshwork of embryonic connective tissue in the mesoderm from which are formed the connective tissues of the body, and also the blood vessels and lymphatic vessels. Mesothelioma: Malignant tumour of the mesothelium (simple squamous epithelium that lines pleural cavities) usually of lung, caused by exposure to asbestos. Metabolite: Any substance produced by metabolism. Metalloproteinase: Peptide hydrolases, which use a metal in the catalytic mechanism. This group of enzymes is inactivated by metal chelators. Metastasis: Spread of malignant cells from a primary site to a distant part of the body. Metazoa: Multicelluar animals whose cells become differentiated to form tissues. Methotrexate: A folic acid antagonist; used as anticancer agent in the treatment of acute leukemia, cancer of the breast, testis and many other cancers. Mevalonic acid: A six carbon organic compound that is a precursor of cholesterol biosynthesis. MHC Antigen: Major histocompatibility protein present on cell surface. There are two types of MHC proteins, class I, present almost on all cell surfaces, and class II, present on the cells of the immune system and macrophages. Microsatellite: Short DNA sequences of di-or trinucleotide repeats of variable length distributed widely throughout the genome. Microsomal Enzymes: Enzymes present in the membranous structure called microsomes in higher organisms. They are mainly involved with the metabolism of detoxification. In such a process some compounds are converted into carcinogens. Microsome: Irregular membranous structures in the cytoplasm containing various enzymes. In these structures some noncarcinogenic compounds are converted to carcinogens with the help of specific enzymes. These structures are also involved in the detoxification of drugs and other unwanted materials. Microtubules: Slender, tubular structures composed mainly of a specific protein called tubulin, present in the cytoplasm of nearly all cells. They are involved in the maintenance of cell shape and in the formation of spindle fibers of mitosis. Millirad: It is 1/1000th of a rad. Rad stands for radiation absorbed dose and is defined as the dosage of radiation that deposits 1x10-2 J of energy per kilogram of tissue. However, in biological systems the effect of radiation depends on the type of radiation, e.g., alpha, beta or gamma radiation. Minorgroove: Surface of a nucleic acid double helix which is narrower than the major groove and is made up of certain base pair edges (A-N3, T-O2, G-N3 and T-O2, in the case of RNA T-O2 becomes U-O2) Mitochondria: Small spherical to rod-shaped components found in the cytoplasm of cells enclosed in a double membrane. They are the principal sites for the generation of energy from the oxidation of foodstuff, and they contain the enzymes for carbohydrate and fatty acid cycle. Mitochondria also contain DNA and RNA, by means of which they can independently replicate and synthesize some of their proteins. See diagram on Cell. Mitogen: A substance that induces blast transformation; DNA, RNA, and protein synthesis; and proliferation of lymphocytes, for example, pokeweed mitogen, or phytohemagglutinin. Mitotic: Pertaining to mitosis, a method of indirect division of cells by means of which two daughter nuclei receive identical complements of the number of chromosomes characteristic of the somatic cells of the species. Mitotic-spindle: Microtubule fiber that develops during mitosis and participates in pulling the chromosome halves to opposite poles of the cell. See diagram above. Monoclonal Antibody: Chemically and immunologically homogeneous antibodies produced by hybridomas, which are formed by fusion of normal lymphocytes and tumor cells. Monocytes: Mononuclear phagocytic white blood cells Mononucleosis: The presence of an abnormally large number of mononuclear leukocytes (monocytes) on the blood. mRNA: Messenger RNA, a transcript of a gene containing information that is translated to a protein. Mucin: A mucopolysaccharide or glycoprotein, the chief constituent of mucus. Mucositis: Inflammation of mucous membrane. Multidrug resistance: Broad resistance to multiple drugs caused by the presence of high molecular membrane glycoprotein known as P-gp, the product of mdr gene. Multiple Myeloma: Disseminated malignancy of B cells of immune system characterized by multiple bone marrow tumors associated with bone pain, pathologic fracture, excess calcium, and anemia. Depression of immunoglobulin level results in susceptibility to infection. Murine Mab's: Mouse monoclonal antibodies. Mutagen: Physical or chemical agents that cause mutation. Mutagens can cause cancer but all mutagens are not carcinogens. Mutagenesis: Production of change in the gene. Mutation: Changes in base composition of DNA. Mutation in sex cells can be inherited. Mycobacterium: A class of gram-positive, aerobic, slow-growing bacterium. It has many species; one of them causes tuberculosis. Myelocyte: Precursor of a specific white blood cell type (granulocyte) and in the stage of development when differentiation into cytoplasmic granules has begun. Myelocytic Leukemia: Leukemia in which predominating cells affected are monocytes. Myelodysplasia: Defective development of any part, especially the lower segments, of the spinal cord. Myelodysplastic syndromes: A group of disorders characterized by low white blood cell counts, low platelet counts, and, in some cases, increased monocytes. The primary problem is in the bone marrow cellularity. Myelogenous Leukemia: Leukemia produced in the bone marrow. Myeloid: Collective term for the nonlymphocyte group of white blood cells. Myeloid Cells: Cells derived from or resembling bone marrow. Myeloma: Cancer of the cells of immune system. Myelomonocytic Leukemia: A type of monocytic leukemia in which predominating cells are of the myeloid series. Myelosuppression: The suppression of bone marrow activity, resulting in reduction in the number of platelets, red cells and white cells found in the circulation. Myelosuppressive: Inhibiting bone marrow activity, resulting in decreased production of blood cells and platelets. Myometrial: Pertaining to the myometrium, the smooth muscle coat of the uterus, which forms the main mass of the organ. Myotonic dystrophy: A rare slowly progressive, hereditary disease transmitted as an autosomal dominant trait characterized by myotonia (tonic spasm of muscle) followed by atrophy of the muscle, cataracts, hypogonadism, cardiac abnormalities.