Correlation between the low marrow blast cutpoint and WHO classification for myelodysplastic syndromes

To the Editor: The most widely used prognostic classification system used for myelodysplastic syndromes (MDS) is the International Prognostic Scoring System (IPSS) (1). Greenberg et al. (2) recently proposed a Revised IPSS (IPSS-R). Bone marrow (BM) cytogenetics, BM blast percentages, and cytopenias remained the basis of this new system. A low marrow blast cutpoint (2%) was added to novel components of the IPSSR. In the IPSS-R, the <5% marrow blast category was split between 0– 2% and >2–<5%. The World Health Organization (WHO) classification-based Prognostic Scoring System (WPSS) proposed by Malcovati et al. (3) was published long before the IPSS-R adopted the split of blasts <5% into two groups. The WHO category according to the WHO classification 3rd edition (4) is included in components of the WPSS, but is not included in IPSS-R components. The low BM blast cutpoint (2%) of IPSS-R is not included in criteria of the WHO category. To clarify the correlation between the low marrow blast cutpoint and WHO category, we compared marrow blast percentages of refractory anemia of the WHO category (WHO-RA) and refractory cytopenia with multilineage dysplasia (RCMD). Data set of our previous study (5) was used for the present analysis. The database consisted of primary untreated MDS patients with refractory anemia according to the French–American–British classification. Patients with MDS associated with isolated del (5q) were excluded from the present analysis. WHO-RA and RCMD patients totaled 238 cases (Japanese 96 cases, German 142 cases) and 448 cases (Japanese 32 cases, German 416 cases), respectively. U.G. and Y.M., who are coauthors of the present analysis, are coauthors of the IPSS-R report. Therefore, some patients of the present analysis may have been included in the IPSS-R report. However, in the IPSS-R report, there is no mention of analysis of the WHO category. Definition of blast cells by Goasguen et al. (6) was used in this study. This definition was adopted in consensus proposals of International Working Group on Morphology of MDS (IWGM-MDS) (7). Continuous data were compared using the nonparametric Mann–Whitney test, and proportions were compared using the chi-square test. The present analysis was approved by the Institutional Review Board of Saitama International Medical Center, Saitama Medical University. Definition of blast cells by Goasguen et al. is simple. In fact, the distinction between blasts and promyelocytes was easy. In addition, we held two times of joint review meetings for making cytomorphologic database. Therefore, we believe that the reliability of the blast percentage is high in present study. In IPSS-R study, it was reported that the split between 0– 2% and >2–<5% was reproducible within the various databases from the different institutions (2). The BM blast percentage of RCMD patients was higher than that of WHORA patients (P = 0.0011). The frequency of patients with BM blast >2–<5% in RCMD was higher than that in WHORA (P = 0.0022) (Table 1). It was reported that RCMD patients had a more unfavorable prognosis than WHO-RA patients (3, 4). Therefore, it seems that the low marrow blast cutpoint (2%) may have prognostic significance.