- A tumor of antibody-producing cells, called plasma cells, that are normally found in the bone marrow.
* * *1. A tumor composed of cells derived from hemopoietic tissues of the bone marrow. 2. A plasma cell tumor. [myelo- + G. -oma, tumor]- Bence Jones m. multiple m. in which the malignant plasma cells excrete only light chains of one type (either κ or λ); lytic bone lesions occur in about 60% of the cases, and light chains (Bence Jones protein) occur in the urine; amyloidosis and severe renal failure are more common than in multiple m.. SYN: L-chain disease, L-chain m..- multiple m., m. multiplex an uncommon disease that occurs more frequently in men than in women and is associated with anemia, hemorrhage, recurrent infections, and weakness. Ordinarily, it is regarded as a malignant neoplasm that originates in bone marrow and involves chiefly the skeleton, with clinical features attributable to the sites of involvement and to abnormalities in formation of plasma protein; characterized by numerous diffuse foci or nodular accumulations of abnormal or malignant plasma cells in the marrow of various bones (especially the skull), causing palpable swellings of the bones, and occasionally in extraskeletal sites; radiologically, the bone lesions have a characteristic punched-out appearance. The m. cells produce abnormal proteins in the serum and urine; those formed in any one example of multiple m. are different from other m. proteins, as well as from normal serum proteins, the most frequent abnormalities in the metabolism of protein being: 1) the occurrence of Bence Jones proteinuria, 2) a great increase in monoclonal γ-globulin in the plasma, 3) the occasional formation of cryoglobulin, and 4) a form of primary amyloidosis. The Bence Jones protein is not a derivative of abnormal serum protein, but seems to be formed de novo from amino acid precursors. SEE ALSO: plasma cell m.. SYN: multiple myelomatosis, myelomatosis multiplex, plasma cell m. (1).- plasma cell m. 1. SYN: multiple m.. 2. plasmacytoma of bone, which is usually a solitary lesion and not associated with the occurrence of Bence Jones protein or other disturbances in the metabolism of protein (as observed in multiple m.). Some observers emphasize that the solitary lesion probably represents an early phase of classic multiple m., or an example of the latter in which only one focus is recognized.
* * *my·e·lo·ma .mī-ə-'lō-mə n, pl -mas also -ma·ta -mət-ə a primary tumor of the bone marrow formed of any one of the bone marrow cells (as myelocytes or plasma cells) and usu. involving several different bones at the same time see MULTIPLE MYELOMA
* * *n.a malignant disease of the bone marrow, characterized by two or more of the following criteria: (1) the presence of an excess of abnormal malignant plasma cells in the bone marrow; (2) typical lytic deposits in the bones on X-ray, giving the appearance of holes; (3) the presence in the serum of an abnormal gammaglobulin, usually IgG (an immunoglobulin; see paraprotein). Bence-Jones protein may also be found in the serum or urine. The patient may complain of tiredness due to anaemia and of bone pain and may develop pathological fractures. Treatment is usually with such drugs as melphalan or cyclophosphamide, with local radiotherapy to particular areas of pain. See also plasmacytoma.
* * *my·elo·ma (mi″ə-loґmə) [myelo- + -oma] 1. a tumor composed of cells of the type normally found in the bone marrow. 2. multiple m.
Medical dictionary. 2011.