Characterization of Terminal Erythroid Differentiation (TED) and Its Prognosis Impact Inpatients with Myelodysplastic Syndrome (MDS)

INTRODUCTION: Culture assays of normal bone marrow (BM) have shown that TED follows a doubling maturation pattern in each erythroid stage from proerythroblast to orthochromatic erythroblast. For a long time, it has been suggested that TED is profoundly abnormal across all myelodysplastic syndrome (MDS) subtypes. Nevertheless, morphologic quantification of cells undergoing TED in BM both from normal and MDS samples has not been systematically assessed, despite the fact morphological analysis still represents the backbone for the diagnosis.

The aims of this study were to describe the pattern of TED by conventional morphology in BM of individuals without myeloid malignancies and in patients with MDS, and to compare clinical characteristics and prognostic features between MDS patients with normal and abnormal TED.

METHODS: Three independent cytologists from three different institutions performed the morphological analysis of erythroid cells in BM smears in a 500-cell differential count from 74 patients diagnosed with lymphoma without BM involvement, and from 284 patients with MDS at diagnosis. TED stages were conventionally classified into proerythroblast (PE), basophilic (BA), polychromatic (POLYS), and orthochromatic erythroblasts (ORTHOS), and percentages were calculated based on the total cell population. Furthermore, flow cytometry analysis was performed on 11 further lymphoma patients without BM involvement, by using specific immunofluorescent probe patterns detected through the DxFLEX© cytometer. Patients with MDS were categorized as: TED-Normal, when total TED made up ≥15% of total BM cells and followed the expected doubling pattern; TED-Incomplete, when total TED were ≥15% but did not follow a doubling pattern; and TED-absent, when total TED composed <15%. Statistical analysis was performed by R (4.2.0).

RESULTS: Morphologic analysis of normal BM confirmed the doubling growth pattern of TED [median PE of 0.8% (0-1.23); BA of 1.8% (1-2.4; ) POLYS of 8% (6.4-10.89) and POLYS of 8% (6.4-10.89)]. Whereas, immunophenotype analysis showed a linear growth pattern [median PE=0.57% (0.54-0.61), BA=1.35% (1.18-1.75), POLYS=2.64% (2.01-3.01), and ORTHOS=3.91% (3.3-5.37), probably explained by the lysis of the late-stage erythroblast cells by the immunophenotype preparation technique.

Among the 284 MDS patients, 211 (75.5%) were TED-Normal, 46 (16.5%) TED-Incomplete, and 22 (8%) TED-Absent. Patients' characteristics are detailed in Table 1. MDS patients with TED-Normal presented significantly higher levels of hemoglobin (99 g/L vs. 89.5 g/L), reticulocytes (56 x10⁹/L vs. 39 x10⁹/L), and a lower percentage of ring sideroblast (0% vs. 26%) compared to TED-Incomplete (Table 1).

Survival analysis showed that MDS patients with TED-Normal had a median OS of 39.03 months (95% IC 29.73-49.13), whereas it was of 23.77 months (95% IC 12.17-38.7) for TED-Incomplete, and 13.23 months (95% IC 7.17-NA) for TED-Absent; [HR 2.2; p=0.00132]. Of note, no OS differences were found between TED-Incomplete and TED-Absent [HR=1.41; p= 0.246] [Figure 2].

CONCLUSION: Morphological analysis is a suitable methodology for the study of TED maturation. Remarkably, 24.5% of patients with MDS presented with an abnormal TED (incomplete or absent) at diagnosis, this being associated with poorer clinical features and outcome. Finally, with the advent of newer erythroid maturation agents, analysis of TED might become paramount for treatment selection and response monitoring of patients with MDS in the near future.

Molero:Oryzon Genomics: Consultancy. Salamero:Abbie, BMS, Novartis: Consultancy, Honoraria. Bosch:Roche: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Karyospharm: Honoraria; Celgene/BMS: Consultancy, Honoraria; Astra Zeneca: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Mundipharma: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Lilly: Consultancy, Honoraria; Beigene: Consultancy, Honoraria.