Multicenter Prospective Evaluation of Diagnostic Potential of Flow Cytometric Aberrancies in Myelodysplastic Syndromes
Authors: Kern Wolfgang , Westers Theresia M. , Bellos Frauke , Bene Marie C , Bettelheim Peter , Eidenschink Brodersen Lisa , Burbury Kate , Chu Sung-Chao , Cullen Matthew , Porta Matteo Della , Dunlop Alan Stewart , Johansson Ulrika , Matarraz Sergio , Oelschlaegel Uta , Ogata Kiyoyuki , Porwit Anna , Preijers Frank W. M. B. , Psarra Katherina , Saft Leonie , Subirá Dolores , Weiss Elisabeth , Van de Loosdrecht Arjan A. 
Published: November 2021

Abstract
Background: Myelodysplastic syndromes (MDS) are considered clonal diseases and are diagnosed according to WHO by cytomorphology and cytogenetics. The diagnostic potential of flow cytometric aberrancies has not yet been comprehensively evaluated.
Aim: Multicenter prospective evaluation of diagnostic potential of flow cytometric aberrancies predefined according to European LeukemiaNet (ELN).
Methods: 1682 patients undergoing diagnostics for suspected MDS according to WHO 2016 criteria were analyzed in parallel by flow cytometry according to ELN recommendations.
Results: Median age was 72 years (18-97). MDS, MPN-RS-T or CMML were confirmed by cytomophology in 1029 (61%) cases, 653 (39%) were non-MDS. IPSS-R data was available in 857 (51%). An overall flow cytometric readout was available in 1679 (99.8%). 1001 (60%) were in agreement with MDS while 678 (40%) were not. Flow cytometric readout significantly correlated with cytomorphologic diagnosis (p&lt;0.001): 850 (51%) were positive by both methods (flow+/cyto+), 502 (30%) were flow-/cyto-, 176 (10%) were flow-/cyto+ and 151 (9%) flow+/cyto-. The rate of flow+ was higher in high-risk MDS (MDS-EB1/2, 92%) and CMML (89%) compared to low-risk MDS (76%). Accordingly, regarding IPSS-R highest frequency of flow+ was found in very high risk (96%) and lowest one in very low risk group (64%).
Non-MDS cases had a fewer myeloid progenitor cells (MPC) (mean±SD, 0.8±0.9%) compared to low-risk MDS (1.7±2.3%, p&lt;0.001), high-risk MDS (6.3±5.0%, p&lt;0.001) and CMML (1.9±2.6%, p&lt;0.001). In particular, MPC &gt;3% was strongly associated with MDS/CMML (286/293, 98%, p&lt;0.001). Antigen expression aberrancies in MPC were more frequent in cases with MDS or CMML than in non-MDS cases but differed between entities with lower frequencies in low-risk MDS cases (table 1).
Neutrophil aberrancies were found more frequently in neoplastic cases than in non-MDS cases (table 1). Again, frequencies of aberrations were higher for high-risk MDS as compared to low-risk MDS while this was not the case for CMML showing frequencies rather similar to low-risk MDS.
Frequencies of aberrancies in monocytes revealed a similar figure as in neutrophils with higher rates in neoplastic cases but clearly significant numbers positive in non-MDS cases. Interestingly, frequencies were not higher in high-risk MDS as compared to low-risk MDS. As anticipated, frequencies were highest in CMML (table 1).
Regarding erythroid cells only an aberrant percentage of them and aberrant CD71 expression were found in a reasonable number of cases. Importantly, rates of positivity were rather high in non-MDS cases which did not differ from CMML cases (table 1).
In order to identify the diagnostic value of each individual aberrancy multivariate analyses were performed in the three subgroups, low-risk MDS, high-risk MDS and CMML, as well as in the total cohort. In low-risk MDS ten aberrancies were independently related to MDS (table 2). Five of these aberrancies were found in MPCs, two each in neutrophils and monocytes and one in erythroid cells. In high-risk MDS 11 aberrancies were independently related to MDS (table 2). Eight were found in MPCs, two in neutrophils, none in monocytes and one in erythroid cells. In CMML 12 aberrancies were independently related to CMML (table 2). Four were found in MPCs, neutrophils and monocytes, respectively, and none in erythroid cells. Considering all these three groups together and all aberrancies identified significantly related to MDS/CMML in at least one group in univariate analysis, multivariate analysis identified 12 aberrancies independently related to MDS/CMML (table 2). Six were found in MPCs, two in neutrophils, three in monocytes and one in erythroid cells.
Taking into consideration only aberrancies independently associated with MDS/CMML, three such aberrancies resulted in an 80% agreement with the cytomorphologic diagnosis of MDS/CMML, i.e. 20% concordantly negative and 60% concordantly positive. Importantly, this applies without need of at least two cell compartments being affected as specified in the ELN recommendations.
Conclusions: This multicenter prospective evaluation confirms the diagnostic potential of flow cytometric aberrancies. A core set of 17 markers identified as independently related to a diagnosis of MDS/CMML is suggested mandatory for flow cytometric evaluation of suspected MDS. An MPC count &gt;3% should be considered indicative of MDS/CMML.
Figure 1 Figure 1.

Disclosures
Kern: MLL Munich Leukemia Laboratory: Other: Part ownership. Eidenschink Brodersen: Hematologics, Inc.: Current Employment, Other: Equity Ownership. Van de Loosdrecht: Celgene: Consultancy, Research Funding; Amgen: Consultancy; Roche: Consultancy; Novartis: Consultancy; Alexion: Consultancy.