INVOLVEMENT OF PERIPHERAL-BLOOD CELLS IN MULTIPLE-MYELOMA - CHROMOSOME CHANGES ARE THE RULE WITHIN CIRCULATING PLASMA-CELLS BUT NOT WITHIN B-LYMPHOCYTES

The mononuclear cells in the peripheral blood are implicated in the my eloma process especially with the presence of peripheral blood plasma cells (PBPC) and clonal B lymphocytes found using phenotypic or gene r earrangement techniques. The purpose of this study was to look for ane uploidy in the two main B cell components of the peripheral blood: PBP C and CD20-positive B lymphocytes, Conventional cytogenetics (CC) or D NA content analysis and fluorescence in situ hybridization (FISH) with centromeric probes were performed on bone marrow plasma cells (BMPC) of 21 patients with multiple myeloma and peripheral blood cells were s tudied as follows: immunostaining to look for PBPC and to assess their number, image analysis cytometry for the determination of their DNA c ontent, and FISH chromosomes analysis. FISH was performed using probes against the chromsomes that were lost or gained in BMPC and was coupl ed with immunostaining of the relevant light chain or CD20 antigen to study PBPC or B lymphocytes, respectively. Monotypic PBPC were found i n 16 patients. Their DNA content was the same or nearly the same as fo r BMPC and they exhibited the same monosomies or trisomies as those fo und within their BM counterpart. By contrast, DNA content of mononucle ar cells other than PBPC was within normal ranges, and in 13 of 15 pat ients CD20-positive B lymphocytes failed to show chromosomal changes b y FISH analysis. In two patients however, a few CD20(+) cells with lym phoid morphology exhibited chromosome changes, hypothesizing that a fe w cytogenetically abnormal B cells without plasmocytic morphology may circulate. From these data, we conclude that PBPC share the same genet ic abnormalities as BMPC and thus belong to the malignant clone, where as most peripheral blood B lymphocytes are unrelated to the tumor clon e.