Clinicopathologic and prognostic features of TdT-negative pediatric B-lymphoblastic leukemia

Terminal deoxynucleotidyl transferase expression in different subtypes of childhood B-cell acute lymphoblastic leukemia

The lack of expression of terminal deoxynucleotidyl transferase (TdT) is frequently associated with KMT2A-rearranged subtype of pediatric acute lymphoblastic leukemia (ALL). However, this association has not been investigated extensively in the Asian population. A retrospective analysis of TdT expression in pediatric B-cell ALL (B-ALL) was performed in patients treated using the Taiwan Pediatric Oncology Group (TPOG) ALL 2002 and 2013 protocols. Among the 331 patients with B-ALL, 12 patients showed TdT negativity at initial diagnosis. Among these, eight patients showed KMT2A rearrangement (66.7%). Other patients showing negative TdT expression had ETV6::RUNX1, MEF2D-rearranged, and other B-ALL subtypes. However, in the context of KMT2A-rearranged B-ALL (n = 20), only eight patients showed TdT negativity. The 5-year event-free survival and overall survival of patients with and without TdT expression were 83.8% versus 46.8% (P <0.001) and 86.3% versus 55.4% (P = 0.004), respectively. Moreover, several aberrant markers, such as CD2, CD56, CD7, and CD117, were rarely expressed in the B-ALL samples, and if expressed, they were enriched in specific genetic subtypes. The results of this study indicate that immunophenotypic features are correlated with specific genetic subtypes of childhood B-ALL.

Increased Incidence of TdT-negative Pre-B Acute Lymphoblastic Leukemia Associated With Poor Prognostic Features Among Mexican Children in Central Mexico

Mexican and Hispanic children in Mexico and the United States, respectively, have the highest incidence and worst outcomes of pre-B acute lymphoblastic leukemia (ALL) compared with other racial/ethnic groups. Terminal deoxynucleotidyl transferase (TdT) is an intranuclear DNA polymerase normally present on immature lymphocytes (TdT-positive) and distinguishes ALL from mature lymphoid malignancies. We performed a multisite retrospective study to determine the incidence of TdT-negative precursor B-cell acute lymphoblastic leukemia (pre-B ALL) among Mexican, Caucasian, and US-born Hispanic children to correlate TdT expression with patient characteristics and known prognostic factors. Fisher exact test was performed for categorical variables and the Wilcoxon rank-sum test was used for continuous variables. TdT-negative pre-B ALL was most frequently identified in patients with National Cancer Institute high-risk disease ( P =0.014). TdT-negative expression was also most frequently associated with hypodiploid pre-B ALL ( P =0.001) and KMT2A gene rearrangement ( P =0.0012). Mexican children had the highest incidence of TdT-negative ALL compared with Caucasians and US Hispanics ( P <0.001), with an increased incidence of poor prognostic features as well. This study demonstrates significant differences in TdT-negative expression, genomic alterations, and leukemic ploidy based on race and ethnicity.

PAX5 and TDT-Negative B-Acute Lymphoblastic Leukemia with Unusual Genetic Mutations: A Case Report

B-acute lymphoblastic leukemia (B-ALL) is commonly encountered in clinical practice. Patients present with increased percentage of lymphoblasts in bone marrow and/or peripheral blood. Immunophenotypic study by flow cytometry or immunohistochemistry is essential to establish the diagnosis. Paired box-5 (PAX5) is a B cell lineage protein and terminal deoxynucleotidyl transferase (TDT) is an immature marker, both of which are routinely tested in the pathologic workup of acute leukemia. In this report, we describe a case of B-ALL in a 37-year-old woman in which both PAX5 and TDT were negative. Next-generation sequencing test detected mutations in DNA methyltransferase 3 α and Fms related receptor tyrosine kinase 3 genes, which are frequently mutated in acute myeloid leukemia rather than B-ALL. The constellation of these rare findings in a single case signifies the importance of examining a wide panel of markers when the diagnosis of ALL is suspected.