Cytogenetic evidence that the malignant event in multiple myeloma occurs in a precursor lymphocyte

Multiple myeloma is traditionally thought of as a disease of plasma cells. Evidence from studies using antiodiotype antibodies, however, suggests that malignant events may take place in a precursor lymphocyte perhaps as early as the pre-B cell. In this study, we present cytogenetic evidence to support the latter view. Peripheral blood was obtained from a patient with plasma cell leukemia and light chain disease. Karyotypic analysis, using Giemsa banding techniques, showed an abnormal karyotype: 44,XY,-6,-8,-13,-16,-22,+mar1,+ mar2,+mar3,del(1)(p22,p32),11p+,13q+,14q+. A suspension culture was established and a plasma cell line was grown. It was characterized by transmission electron microscopy as having an eccentric nucleus, abundant cytoplasm, and extensive endoplasmic reticulum. A subculture of this line was subsequently grown that was characterized by transmission electron microscopy as a lymphoid cell with diminished quantity of cytoplasm without extensive endoplasmic reticulum. Karyotypic analysis of the smaller cell demonstrated a modal number of 88 chromosomes and was a tetraploid derivative of the first. Our study provides cytogenetic evidence that cells with a lymphocytic phenotype show karyotypic abnormalities seen in the malignant plasma cell of the same patient, and thus, can be considered as evidence favoring the initiating cell of plasma cell myeloma as being an early B lymphocyte.