Plasma cell leukaemia of non-producer type with missing light chain gene rearrangement

A case of plasma cell leukaemia of non-producer type is described. The patient presented with typical clinical features of plasma cell myeloma, including multiple osteolytic lesions, hypercalcaemia, renal failure and reduced polyclonal immunoglobulins, except that M-component was not detected in either the serum or urine. Morphological examinations showed a plasmacytoid appearance of the neoplastic cells, while immunological studies failed to detect cytoplasmic immunoglobulin or secretory capacity. The surface phenotype of CD38+, PCA-1+, DR-, CD20-, CD24-, CD9-, CD10- and surface immunoglobulin- was compatible with mature plasma cells. Chromosomal analysis showed the 14q+ marker due to translocation (6;14) and deletion of the short arm of chromosome 1. Analysis of immunoglobulin genes revealed the presence of heavy chain gene rearrangement, but the light chain genes, both kappa and lambda, remained in germline configuration. Such defective immunoglobulin gene rearrangement may be responsible for the failure of immunoglobulin biosynthesis and secretion by the neoplastic plasma cells. Furthermore, it is suggested that the morphological and phenotypic development of B cells may not necessarily depend on immunoglobulin light chain gene rearrangement, and that the oncogenic event in myeloma may occur at an earlier stage of B cell differentiation.