ALL-248 Measurable Residual Disease Assessment by Flow Cytometry in T-Cell Acute Lymphoblastic Leukemia

Abstract

Background Minimal/measurable residual disease (MRD) assessed by multicolor flow cytometry (FCM) is a powerful prognostic indicator for risk stratification in acute leukemia, including T-cell acute lymphoblastic leukemia (T-ALL). MRD-positive status in T-ALL is significantly associated with inferior relapse-free survival and overall survival. Methods A retrospective study was conducted in 68 newly diagnosed cases of T-ALL from January 2022 to December 2022. Diagnosis of T-ALL was made based on morphology, cytochemistry, and flow cytometric immunophenotyping. Based on the diagnostic phenotype, we subclassified the patients into 3 categories: early thymic precursor T-cell ALL (ETP-ALL), near-ETP-ALL or ETP-like ALL, and non–ETP-ALL. Results Patients were immunophenotypically subclassified as ETP-ALL (9, 13.2%), near-ETP-ALL (14, 20.6%), and non–ETP-ALL (45, 66.2%). Median age was12 years (range: 2-62), M:F ratio was 4.2:1. Median hemoglobin was 85 g/L (range: 4.1-14.2 g/L), TLC was 31.48x10/L (range: 0.54-1500x10/L), platelets were 58x10/L (range: 5-665x10/L), LDH was 1079 IU/L (range: 144-12835 IU/L) with peripheral blood and bone marrow blast percentage 76% (0-98%) and 90% (70-98%), respectively. In diagnostic samples, dim to moderate expression of sCD3 was noted only in 4.4%, CD4 in 52.9%, CD8 in 45.6%; 35.3% samples were dual-positive for CD4/CD8, and 33.8% were dual-negative for CD4/CD8 expression. Markers of immaturity like CD1a, CD10, and CD34 were positive in 36.8%, 33.8%, and 44.1%, respectively. One or more myeloid markers were positive in 25.0% of cases. We also noted the expression of B-cell markers like CD19 and cCD79a in a small subset of samples (4.4% and 11.8%, respectively). End-ofinduction (EOI) MRD was available for 73.5% of patients (n=50). MRD was detectable in 28% of patients, with a median MRD level of 0.49% and a range of 0.02–90.0%, including 3 patients who were not in remission and had ≥5% residual blasts in MRD evaluation. In MRD evaluation, dual CD4/CD8 negativity followed by bright expression of CD7 was the common abnormality. Conclusions The inclusion of CD4 and CD8, along with other T-cell markers, is highly useful in T-ALL MRD assessment. Baseline immunophenotyping is not required in all cases of T-ALL MRD evaluation. In MRD evaluation, dual CD4/CD8 negativity followed by bright expression of CD7 was the common abnormality.