Relevance of flow cytometric categorization and end-of-induction measurable residual disease assessment in pediatric and adult T-lymphoblastic leukemia patients.

Background: T-lymphoblastic leukemia (T-ALL) patients expressing myeloid/stem cell antigens are classified as early T-cell precursor lymphoblastic leukemia (ETP-ALL) or near-ETP-ALL. Methods: Clinico-laboratory profiles, flow cytometric end-of-induction measurable residual disease (EOI-MRD), and survival of treatment naïve T-ALL patients were analyzed according to their immunophenotypic subtypes. Results: Among 81 consecutive T-ALL patients diagnosed, 21% (N=17) were ETP-ALL and 19% (N=15) were near-ETP-ALL. EOI-MRD was detectable in 39% of the 59 samples tested (31.6% of pediatric samples and 52.4% of adult samples). The frequency of EOI-MRD positivity was significantly higher among ETP-ALL (75%, P=0.001) and near-ETP-ALL (71%, P=0.009) patients compared to that in conventional-T-ALL (con-T-ALL) patients (22.5%). CD8 (P=0.046) and CD38 (P=0.046) expressions were significantly upregulated in the EOI blasts of con-T-ALL and ETP-ALL samples, respectively. The 2-year rates of overall (OS), relapse-free (RFS), and event-free survival (EFS) among the T-ALL patients (pediatric vs. adult) was 79.5% vs. 39.8% (P<0.001), 84.3% vs. 60.4% (P=0.026), and 80.3% vs. 38% (P<0.001), respectively. Univariate analysis revealed that 2-year EFS and RFS of pediatric T-ALL patients was independent of T-ALL subtype and was influenced only by EOI-MRD status. However, 2-year OS, RFS, and EFS among adult T-ALL patients were EOI-MRD independent and influenced only by the near-ETP-ALL phenotype. Conclusion: Two-year survival among pediatric and adult T-ALL patients is attributed to EOI-MRD status and near-ETP-ALL phenotype, respectively.