Absolute number of circulating CD34(+) cells is abnormally low in refractory anemias and extremely high in RAEB and RAEB-t; novel pathologic featuresof myelodysplastic syndromes identified by highly sensitive flow cytometry

We scored absolute numbers of circulating CD34(+) cells by a highly sensiti ve triple-color flow cytometric analysis using CD45 monoclonal antibody, CD 34 monoclonal antibody and propidium iodide. Forty-one patients with MDS (R A: 27, RARS: 1, RAEB: 6, RAEB-t: 3,CMML: 4), 12 patients with aplastic anem ia (AA) and 36 age-adjusted normal subjects were studied. RA had significan tly decreased numbers of cells expressing CD34 (0.21 +/- 0.29 x 10(6)/l) co mpared with normal subjects (0.81 +/- 0.36 x 10(6)/l)(P < 0.001). This low number of CD34(+) cells in RA resembles the case of AA (0.39 +/- 0.73 x 10( 6)/l). In light-scatter analysis, the CD34(+) cells of RA patients were dis tributed mainly in low forward scatter (FSC) (lymphocyte region). In contra st, the CD34+ cell counts were extremely high in patients with RAEB (46.54 +/- 71.37 x 10(6)/l) and RAEB-t (57.00 +/- 52.36 x 10(6)/l) (P < 0.001) and the CD34(+) cells were observed in high FSC (blast region). CMML patients showed moderately increased numbers of CD34(+) cells (3.69 +/- 4.64 x 10(6) /l). Thus, there was a distinct difference in cell size and number of circu lating CD34(+) cells between RA and RAEB/RAEB-t. In univariate and multivar iate analysis, a high CD34(+) cell count (greater than or equal to 1.0 x 10 (6)/l) was a poor prognostic factor. This method allows one to distinguish RA from other MDS subtypes more reliably than by morphology alone and provi des early signs of progression to acute leukemia. (C) 2000 Elsevier Science Ltd. All rights reserved.