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Macroglobulinemia: An increase of one type of immunoglobulin referred to as macroglobulin. It differs from other immunoglobulin molecules in being five times the size of standard-sized immunoglobulin. In this disease state, B-lymphocytes produce an excess amount of this type of immunoglobulin. The malignant form of the disease, a type of chronic B-Lymphocyte leukemia, is referred to as Waldenström's macroglobulinemia, after the Swedish hematologist who described the first cases of the disease.

Macrophage: A type of tissue cells that is derived from the blood monocyte. The monocyte migrates from the blood into tissues where it transforms into a macrophage. Macrophages are present in most tissues. The cell takes many forms and has several functions. Three examples of macrophage functions are 1) ingest and degrade debris during tissue repair and remodeling, 2) ingest and kill or contain the growth of microorganisms, and 3) process and present antigens to lymphocytes.

Magnetic Resonance Imaging (MRI): This technique provides detailed images of body structures. It differs from a CT scan in that the patient is not exposed to X-rays. The signals generated in the tissues in response to a magnetic field produced by the instrument are converted by computer into images of body structures. Thus, the size and a change in size of organs or tumor masses, such as the lymph nodes, liver and spleen can be measured.

Maintenance Treatment: Treatment given for a period of months or years to maintain remission and further decrease residual leukema or lymphoma cells in the body. In acute lymphoblastic leukemia, for example, treatment is maintained for several years after remission is induced.

Malignancy: A term with several meanings. In one usage, it is a synonym for cancer, as in “My friend was diagnosed with a malignancy”. In another usage it indicates a progressive, difficult to manage form of cancer, as in “Was the cancer benign or malignant?”

Mast T-cell: A cell that is derived from the pluripotential lymphohematopoietic stem cell. It traverses the blood in such small numbers that it is not recognized as a blood cell. It enters the tissues and in those sites is apparent because of its large and numerous granules, which when stained in slides of tissue samples have a characteristic deep blue-purple color. In allergic reactions, it is the source of histamine and other chemicals that causes many of the symptoms of allergy.

Megakaryocyte: A very large (giant) cell in the marrow. It sheds its cytoplasm in small fragments, which become the blood platelets.

Mitosis: The process by which a single cell divides into two cells. Synonyms for mitosis are cell division, cell replication, cell growth or cell proliferation.

Monoclonal: The cells that are derived from a single common ancestor cell are part of a single clone. For example, all leukemias, lymphomas, and myeloma are the result of the malignant transformation of a single cell and are monoclonal diseases. If those cells are immunoglobulin-producing cells (B-lymphocytes or their derivative plasma cells), the immunoglobulin protein they make is of one restricted type, referred to as monoclonal protein. The group of neoplastic diseases that form monoclonal proteins are referred to as monoclonal gammopathies. (See Clonal (monoclonal))

Monoclonal Antibodies: Antibodies made by cells belonging to a single clone. These highly specific antibodies can be produced in the laboratory. They are very important reagents for identifying and classifying disease by immunophenotyping cells. They have clinical applications for targeted delivery of drugs to leukemia or lymphoma cells and can be used to purify cells used for stem cell transplants.

Monoclonal Disease: All neoplasms are monoclonal. Contrariwise, all monoclonal tissue alterations are neoplasms. Benign as well as malignant cancers are monoclonal, that is they are the result of the neoplastic transformation of a single cell. That single cell multiplies and forms the tumor. Thus the principal genetic characteristics of all the cells in the clone are identical. The leukemias, lymphomas, and myeloma are, as all neoplasms, monoclonal.

Monoclonal Gammopathy: The term applied to a group of diseases that result from the transformation of a B-Lymphocyte or its derivative cell, the plasma cell. One of the key features of these diseases is the production and presence in the blood, and/or the urine of a protein called a monoclonal immunoglobulin. This protein is in the portion of the plasma proteins that are known as the gamma globulins. Hence, the term “gammopathy,” in which the prefix “gammo” refers to a gamma globulin and the suffix “-pathy,” (derived from the Greek word for abnormality or disease), refers to “disorders of ”. These cancers, in which the cells make a monoclonal immunoglobulin, are also referred to as gammopathies. These diseases range from a benign form called “essential monoclonal gammopathy” to a malignant form called “myeloma.”

Monocytes: A type of white cell that represents about five to ten percent of the cells in normal human blood. The monocyte, along with the neutrophil, are the two major microbe-eating and killing cells in the blood. When monocytes leave the blood and enter the tissue they are converted to macrophages. The macrophage is the monocyte in action and can combat infection in the tissues, can ingest dead cells (scavenger), and can assist T-lymphocytes in their immune functions.

Monocytic Leukemia: A type of acute leukemia in which the leukemic cells have the appearance or react with special stains characteristic of monocytes.

Monosomy: Term that indicates the loss of one chromosome of a pair. Monosomy 7, for example, indicates that the blood cells of the patient have lost one of two number 7 chromosomes. This abnormality occurs in myelomonocytic leukemia.

Mortality: The number of individuals that die as a result of a specific disease or group of diseases each year. When expressed as a rate, it is the number of deaths during that time period per standard unit of population. E.g., 4 cases/ 100,000 population per year.

Mucosa-Associated Lymphoid Tissue (MALT) Lymphomas: The term used for lymphomas that originate in the lining of the intestinal tract or closely associated glandular tissue. The stomach is the most frequent site of this type of lymphoma. The bacterium that causes stomach ulcers, Helicobacter pylori can result in an immune reaction in the lining of the stomach that increases the risk of a lymphoma developing in that site. These lymphomas are often only slowly progressive and tend to remain localized. In some cases of gastric lymphoma, antibiotic treatment of the bacteria can lead to remission of the lymphoma.

Mucositis: Inflammation of the mucous membranes. A complication of some forms of chemotherapy which leads to painful, ulceration of the lining of the mouth, throat or other mucous membranes.

Mucous Membranes or Mucosa: The lining of tubular structures such as the inner lining of the mouth, nose, sinuses, esophagus, vagina, and many others. These linings require new cells to be made to replace those that drop off. This replacement is a normal process and keeps the lining intact and moist. Patients who receive radiation or cytotoxic drugs that block cells from dividing prevent the replacement of lost T-cells and the linings become dry, defective, and may ulcerate. This change can be painful such as when mouth ulcers develop. The loss of what is referred to as the “barrier function” of mucous membranes permits microbes to enter the tissue or blood, which may lead to infection.

Multidrug Resistance: A characteristic of cells that makes them resistant to the effects of several different classes of drugs. There are several forms of drug resistance.They each are determined by genes that govern how the cell will respond to the chemical agents. One type of multidrug resistance (or MDR) involves the ability to eject several drugs out of cells. The cell outer wall or membrane of the cell contains a pump that ejects chemicals, preventing them from reaching a toxic concentration. The resistance to drugs can be traced to the expression of genes that direct the formation of high amounts of the protein that prevents the drugs from having their effects on the malignant T-cells. If the gene or genes involved are not expressed or are weakly expressed, the cells are more sensitive to the drug's effect. If the genes are highly expressed, the cells are less sensitive to the drug's effect.

Mutation: An alteration in a gene that results from a change to a part of the stretch of DNA that represents a gene. A “germ cell mutation” is present in the egg or the sperm and can be transmitted from parent(s) to offspring. A “somatic cell mutation” occurs in a specific tissue cell and can result in the growth of the specific tissue cell into a tumor. Most cancers start after a somatic mutation. In leukemia, lymphoma or myeloma, a primitive marrow or lymph node cell undergoes a somatic mutation(s) that leads to the formation of a tumor. In these cases, the tumors are usually widely distributed when detected; they involve the marrow of many bones or involve lymph nodes in several sites, usually.

Mycosis Fungoides: see Cutaneous T-cell Lymphoma

Myelodysplasia or Myelodysplastic Syndrome: A group of neoplasms that originate in a primitive multipotential hematopoietic cell. About half of the cases are mild to moderate anemias accompanied by mild to moderately reduced white cell and platelet counts. Often, these are not progressive but they have a heightened propensity to evolve into acute myelogenous leukemia. The other half of the cases are a type of low blast count leukemia that may be associated with severe white cell and platelet deficits. Many of the patients affected require transfusion therapy, have a propensity to infection or to bleeding, and frequently progress to more overt leukemia. These disorders can occur at any age but are most common after age 60 years.

Myelofibrosis: A term that means the prominent replacement of the marrow by fibrous tissue. Fibrous tissue is composed of fibroblasts and the fibers they make, such as collagen. The disease idiopathic myelofibrosis or agnogenic myeloid metaplasia is a neoplastic disorder manifested by anemia and elevated white cell and platelet counts. The spleen is enlarged, often dramatically so. The abnormal megakaryocytes in the marrow release factors that stimulate marrow fibroblasts to proliferate and elaborate fibrous tissue (collagen fibers). The proliferation of fibroblasts is a secondary reaction, not a part of the cancer.

Myelogenous (syn. Myeloid, Myelocytic): The term's literal derivation is "originating from or produced in the marrow". It is applied to leukemias that originate in a marrow stem cell or early marrow progenitor cell, especially acute and chronic myelogenous leukemia. It also distinguishes the myelogenous leukemias, which originate in a cell that is in the blood cell-forming lineages and usually do not affect T-lymphocytes overtly, from those that originate in a lymphocyte, e.g. acute and Chronic Lymphocytic Leukemia. Myeloid and myelocytic are synonymous terms and the designations acute or chronic myeloid or myelocytic leukemia are used by some but are not the preferred terms.

Myeloma: A neoplasm of B-lymphocytes that manifests itself as the derivative cells referred to as plasma cells. The disease usually starts in the marrow, which is replaced by malignant plasma cells. The malignant plasma cells make a monoclonal immunoglobulin, the detection of which may be very helpful in diagnosis. The cells secrete chemicals that stimulate the over activity of bone-dissolving cells, called osteoclasts, leading to osteoporosis and brittle bones that fracture easily.

Myeloma Cells: These are malignant plasma cells that are the hallmark of myeloma. Their appearance may be similar to normal plasma cells but they are present in increased numbers.

Myeloproliferative Disorders: A group of disorders characterized by the over- production of blood cells by the marrow. (See Essential thrombocythemia, polycythemia vera, chronic myelogenous leukemia.)