Implementation of Diagnostic Flow Cytometry Allows for the Dissection of Age Related Loss of Y Chromosome from Myelodysplastic Syndrome (MDS)

Loss of Y chromosome (-Y) is described as an age related cytogenetic polymorphism as well as an abnormality associated with clonal diseases mainly Myelodysplastic Syndromes (MDS) reported in up to 15% of these patients. However, it often remains an uncertainty dissecting these two conditions especially in patients with mild dysplasia and a low percentage of abnormal metaphases. The aim of our study was to investigate whether flow cytometry (FCM) allows for a valid discrimination between MDS and age related presence of a loss of Y chromosome.

Bone marrow aspirates of 46 patients, suspicious for MDS, with a median age of 76 years and a cytogenetically detected -Y as single abnormality (>75% threshold for assignment to MDS; Wiktor et al. 2011) were investigated. According to cytomorphology MDS could be diagnosed in 26 patients (IPSS-R verylow/low=22, intermediate=3, high/very high=1) and CMML in 6 patients. MDS was excluded in 14 patients (11 IDUS, 1 aplastic anemia, and 2 pts. with reactive changes only). Further routine diagnostic procedures included FCM according to WHO and ELNet iMDS-Flow criteria. Thus, FCM was performed using an 8-color antigen panel measured on a FACS-Canto II cytometer. MDS were defined according to the current FCM-scores developed by Wells et al. (normal/mild: 0-1, moderate: 2-3, or severe: > 4; Blood 2003) and Ogata et al. (low: 0-1, high: >1; Haematologica 2009). In case of an intermediate Wells-score only, we demanded cross lineage antigen expression in myeloid progenitors as criteria for MDS/CMML.

The median percentage of abnormal metaphases presenting with -Y was 52% (range: 12%-100%). Applying the above mentioned threshold of 75% abnormal metaphases as criteria for the presence of MDS, only 14 patients (30%) could clearly be allocated to MDS. Because of the present diagnostic incertainty we performed a comprehensive FCM investigation, applying Wells- and Ogata-Score. Thus, in 26 patients (63%) MDS was likely applying FCM. Furthermore, 4 patients with a normal/mild Wells-score plus a low Ogata-score were considered as "non-MDS". Applying cytomorphology 70% (32/46) of all -Y patients have been diagnosed as MDS.

Of note, MDS diagnosis could be made by FCM or cytomorphology in an equal extent in the groups of more vs. less of 75% cytogenetically abnormal metaphases: 64% vs. 63% and 86% vs. 63%, respectively. Finally, we searched for patients meeting FCM plus cytomorphologic MDS criteria. Of importance, even in the group with less abnormal metaphases 50% of the patients showed a concordant FCM and cytomorphologic assignment to MDS or non-MDS vs. 64% concordance in the high cytogenetically aberrant group.

Patients with a loss of Y chromosome as single cytogenetic abnormality often meet FCM and cytomorphologic criteria for MDS diagnosis independent from the load of abnormal metaphases. This study demonstrates that FCM can significantly contribute to MDS diagnosis in this specific subgroup of patients with -Y and often only mild dysplasia.