[Immunology of myeloma].

Multiple myeloma (MM) is the most common malignant plasma cell dyscrasia. It is defined as the malignant expression of clonal expansion (in blood and bone marrow) of idiotypic B lymphoid cells (B id+) with proliferation, asynchronic maturation, and abnormal secretion of idiotypic plasma cells, initially maintained in the bone marrow. Malignancy includes: suppression of nonidiotypic (= polyclonal) B cell activation, suppression of normal hematopoiesis, and excessive osteoclastic resorption, via the production of osteoclast activating factors by myeloma cells. In MM, tumor growth is initially very slow in bone marrow (= chronic phase), controlled by chemotherapy or spontaneously controlled (= indolent variant). Terminal disease is marked by uncontrolled and fast tumor growth with extramedullary involvement of tumor cells (= fulminant or acute phase). Clonal evolution with chromosomal changes (chromosomes 1, 11, 14) is generally involved in the growth pattern changes. The nature of the oncogenic event and of the myeloma stem cell remains unknown.