CLONAL CIRCULATING CELLS ARE COMMON IN PLASMA-CELL PROLIFERATIVE DISORDERS - A COMPARISON OF MONOCLONAL GAMMOPATHY OF UNDETERMINED SIGNIFICANCE, SMOLDERING MULTIPLE-MYELOMA, AND ACTIVE MYELOMA

The blood of most patients with active multiple myeloma (MM) contains cells related to the bone marrow tumor. However, identifying clonal ce lls in the blood of patients with monoclonal gammopathy of undetermine d significance (MGUS) has been difficult. In this study, we analyzed b lood mononuclear cells (BMNCs) from 16 patients with MGUS, 2 with amyl oidosis, 8 with smoldering MM (SMM), 2 with indolent MM (IMM), and 15 with active MM using three different methods to detect and quantitate clonal cells, ie, immunofluorescence microscopy (IM) for monoclonal pl asma cells, three-color flow cytometry (FC) for CD38(+)CD45(-)CD45(dim ) cells, and the allele-specific oligonucleotide polymerase chain reac tion (ASO-PCR). Using ASO-PCR, we were able to detect clonal cells in the blood in 13 of 16 patients with MGUS, 2 of 2 with amyloid, 6 of 8 with SMM, 2 of 2 with IMM, and 13 of 15 with MM. In 9 of the 13 patien ts with MGUS with blood involvement, the number of clonal cells was ve ry small (<0.04% of the BMNCs). The median percentage of clonal cells as determined by ASO-PCR was 0.02 for MGUS, 0.02 for SMM, and 0.24 for MM. Clonal plasma cells or CD38(+)CD45(-)CD45(dim) cells were identif ied by IM or FC in 6 of 16 MGUS patients, 4 of 8 with SMM, and 11 of 1 5 with MM. In all cases in which IM or FC detected clonal cells, the A SO-PCR was positive, This study shows that, by using ASO-PCR, clonal c ells can be found at very low levels in the blood in most patients wit h MGUS. However, the number of clonal cells in the blood of MGUS patie nts is less than those with overt MM (P = .006). In contrast to MGUS, patients with active MM are more likely to have identifiable clonal ci rculating plasma cells (P = .05). (C) 1996 by The American Society of Hematology.